board: arm: Add support for apollo4p_blue_kxr_evb board.

Add devicetree, Kconfig and doc for Ambiq Apollo4 Blue Plus KXR EVB board.

Signed-off-by: Aaron Ye <aye@ambiq.com>

boards/arm/apollo4p_blue_kxr_evb/Kconfig.board

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+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) 2023 Ambiq Micro Inc. <www.ambiq.com>
+
+config BOARD_APOLLO4P_BLUE_KXR_EVB
+	bool "Ambiq Apollo4 Blue Plus KXR Evaluation Board"
+	depends on SOC_APOLLO4P_BLUE

boards/arm/apollo4p_blue_kxr_evb/Kconfig.defconfig

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+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) 2023 Ambiq Micro Inc. <www.ambiq.com>
+
+config BOARD
+	default "apollo4p_blue_kxr_evb"
+	depends on BOARD_APOLLO4P_BLUE_KXR_EVB

boards/arm/apollo4p_blue_kxr_evb/apollo4p_blue_kxr_evb-pinctrl.dtsi

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+/*
+ * Copyright (c) 2023 Ambiq Micro Inc. <www.ambiq.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <dt-bindings/pinctrl/ambiq-apollo4-pinctrl.h>
+
+&pinctrl {
+	uart0_default: uart0_default {
+		group1 {
+			pinmux = <UART0TX_P12>;
+		};
+		group2 {
+			pinmux = <UART0RX_P47>;
+			input-enable;
+		};
+	};
+};

boards/arm/apollo4p_blue_kxr_evb/apollo4p_blue_kxr_evb.dts

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+/dts-v1/;
+#include <ambiq/ambiq_apollo4p_blue.dtsi>
+
+#include "apollo4p_blue_kxr_evb-pinctrl.dtsi"
+
+/ {
+	model = "Ambiq Apollo4 Blue Plus KXR evaluation board";
+	compatible = "ambiq,apollo4p_blue_kxr_evb";
+	chosen {
+		zephyr,itcm = &tcm;
+		zephyr,sram = &sram0;
+		zephyr,flash = &flash0;
+		zephyr,console = &uart0;
+		zephyr,shell-uart = &uart0;
+		zephyr,uart-pipe = &uart0;
+	};
+	aliases {
+		watchdog0 = &wdt0;
+	};
+
+};
+
+&uart0 {
+	current-speed = <115200>;
+	pinctrl-0 = <&uart0_default>;
+	pinctrl-names = "default";
+	status = "okay";
+};
+
+&counter0 {
+	status = "okay";
+};
+
+&wdt0 {
+	status = "okay";
+};

boards/arm/apollo4p_blue_kxr_evb/apollo4p_blue_kxr_evb.yaml

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+identifier: apollo4p_blue_kxr_evb
+name: Apollo4 Blue Plus KXR EVB
+type: mcu
+arch: arm
+ram: 2816
+flash: 1952
+toolchain:
+  - zephyr
+  - gnuarmemb
+supported:
+  - uart
+testing:
+  ignore_tags:
+    - net

boards/arm/apollo4p_blue_kxr_evb/apollo4p_blue_kxr_evb_defconfig

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+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) 2023 Ambiq Micro Inc. <www.ambiq.com>
+
+CONFIG_SOC_SERIES_APOLLO4X=y
+CONFIG_SOC_APOLLO4P_BLUE=y
+CONFIG_CONSOLE=y
+CONFIG_UART_CONSOLE=y
+CONFIG_SERIAL=y
+CONFIG_UART_INTERRUPT_DRIVEN=y

boards/arm/apollo4p_blue_kxr_evb/board.cmake

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+# Copyright (c) 2023 Ambiq Micro Inc. <www.ambiq.com>
+# SPDX-License-Identifier: Apache-2.0
+
+board_runner_args(jlink "--device=AMAP42KK-KBR" "--iface=swd" "--speed=1000")
+
+include(${ZEPHYR_BASE}/boards/common/jlink.board.cmake)

boards/arm/apollo4p_blue_kxr_evb/doc/index.rst

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+.. _apollo4p_blue_kxr_evb:
+
+Ambiq Apollo4 Blue Plus KXR EVB
+###############################
+
+Apollo4 Blue Plus KXR EVB is a board by Ambiq featuring their ultra-low power Apollo4 Blue Plus SoC.
+
+.. image:: ./apollo4-blue-plus-kxr-soc-eval-board.jpg
+   :align: center
+   :alt: Apollo4 Blue Plus KXR EVB
+
+Hardware
+********
+
+- Apollo4 Blue Plus SoC with upto 192 MHz operating frequency
+- ARM® Cortex® M4F core
+- 64 kB 2-way Associative/Direct-Mapped Cache per core
+- Up to 2 MB of non-volatile memory (NVM) for code/data
+- Up to 2.75 MB of low leakage / low power RAM for code/data
+- 384 kB Tightly Coupled RAM
+- 384 kB Extended RAM
+- Bluetooth 5.1 Low Energy
+
+For more information about the Apollo4 Blue Plus SoC and Apollo4 Blue Plus KXR EVB board:
+
+- `Apollo4 Blue Plus Website`_
+- `Apollo4 Blue Plus Datasheet`_
+- `Apollo4 Blue Plus KXR EVB Website`_
+
+Supported Features
+==================
+
+The Apollo4 Blue Plus KXR EVB board configuration supports the following hardware features:
+
++-----------+------------+-------------------------------------+
+| Interface | Controller | Driver/Component                    |
++===========+============+=====================================+
+| MPU       | on-chip    | memory protection unit              |
++-----------+------------+-------------------------------------+
+| NVIC      | on-chip    | nested vector interrupt controller  |
++-----------+------------+-------------------------------------+
+| SYSTICK   | on-chip    | systick                             |
++-----------+------------+-------------------------------------+
+| STIMER    | on-chip    | stimer                              |
++-----------+------------+-------------------------------------+
+| GPIO      | on-chip    | gpio                                |
++-----------+------------+-------------------------------------+
+| UART      | on-chip    | serial                              |
++-----------+------------+-------------------------------------+
+| WDT       | on-chip    | watchdog                            |
++-----------+------------+-------------------------------------+
+| RADIO     | on-chip    | bluetooth                           |
++-----------+------------+-------------------------------------+
+
+The default configuration can be found in the defconfig file:
+``boards/arm/apollo4p_blue_kxr_evb/apollo4p_blue_kxr_evb_defconfig``.
+
+Programming and Debugging
+=========================
+
+Flashing an application
+-----------------------
+
+Connect your device to your host computer using the JLINK USB port.
+The sample application :ref:`hello_world` is used for this example.
+Build the Zephyr kernel and application, then flash it to the device:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/hello_world
+   :board: apollo4p_blue_kxr_evb
+   :goals: flash
+
+.. note::
+   `west flash` requires `SEGGER J-Link software`_ and `pylink`_ Python module
+   to be installed on you host computer.
+
+Open a serial terminal (minicom, putty, etc.) with the following settings:
+
+- Speed: 115200
+- Data: 8 bits
+- Parity: None
+- Stop bits: 1
+
+Reset the board and you should be able to see on the corresponding Serial Port
+the following message:
+
+.. code-block:: console
+
+   Hello World! apollo4p_blue_kxr_evb
+
+.. _Apollo4 Blue Plus Website:
+   https://ambiq.com/apollo4-blue-plus/
+
+.. _Apollo4 Blue Plus Datasheet:
+   https://contentportal.ambiq.com/documents/20123/388410/Apollo4-Blue-Plus-SoC-Datasheet.pdf
+
+.. _Apollo4 Blue Plus KXR EVB Website:
+   https://www.ambiq.top/en/apollo4-blue-plus-kxr-soc-eval-board
+
+.. _SEGGER J-Link software:
+   https://www.segger.com/downloads/jlink
+
+.. _pylink:
+   https://github.com/Square/pylink