soc: esp32s2: add initial soc support files for esp32s2

by adding specific soc files for esp32s2 bring-up, such as:
- linker script
- soc initialization code
- initial device tree source files
- esp32s2 saola board support.

Signed-off-by: Glauber Maroto Ferreira <glauber.ferreira@espressif.com>

soc/xtensa/esp32s2/Kconfig.defconfig

@@ -0,0 +1,29 @@
+# ESP32S2 board configuration
+
+# Copyright (c) 2021 Espressif Systems (Shanghai) Co., Ltd.
+# SPDX-License-Identifier: Apache-2.0
+
+if SOC_ESP32S2
+
+config SOC
+	default "esp32s2"
+
+config GEN_ISR_TABLES
+	default y
+
+config GEN_IRQ_VECTOR_TABLE
+	default n
+
+config XIP
+	default n
+
+config ISR_STACK_SIZE
+	default 2048
+
+config IRQ_OFFLOAD_INTNUM
+	default 7
+
+config MP_NUM_CPUS
+	default 1
+
+endif