dts: bindings: Add bindings for Semtech SX126x

Add device tree bindings for the Semtech SX1261 and SX1262
radios. These will be used by Zephyr's LoRa drivers.

Signed-off-by: Andreas Sandberg <andreas@sandberg.pp.se>

dts/bindings/lora/semtech,sx1261.yaml

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+# Copyright (c) 2020 Andreas Sandberg
+# SPDX-License-Identifier: Apache-2.0
+
+description: Semtech SX1261 LoRa Modem
+
+compatible: "semtech,sx1261"
+
+include: semtech,sx126x-base.yaml

dts/bindings/lora/semtech,sx1262.yaml

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+# Copyright (c) 2020 Andreas Sandberg
+# SPDX-License-Identifier: Apache-2.0
+
+description: Semtech SX1262 LoRa Modem
+
+compatible: "semtech,sx1262"
+
+include: semtech,sx126x-base.yaml

dts/bindings/lora/semtech,sx126x-base.yaml

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+# Copyright (c) 2019 Manivannan Sadhasivam
+# Copyright (c) 2020 Andreas Sandberg
+# SPDX-License-Identifier: Apache-2.0
+
+include: spi-device.yaml
+
+properties:
+    reset-gpios:
+      type: phandle-array
+      required: true
+      description: |
+        GPIO connected to the modem's NRST signal.
+
+        This signal is open-drain, active-low as interpreted by the
+        modem.
+
+    busy-gpios:
+      type: phandle-array
+      required: true
+      description: |
+        GPIO connected to the modem's BUSY signal.
+
+    antenna-enable-gpios:
+      type: phandle-array
+      required: false
+      description: |
+        Antenna power enable pin.
+
+    dio1-gpios:
+      type: phandle-array
+      required: true
+      description: |
+        GPIO connected to DIO1. This GPIO will be used as a generic
+        IRQ line from the chip.
+
+    dio2-tx-enable:
+      type: boolean
+      required: false
+      description: |
+        Use DIO2 to drive an RF switch selecting between the TX and RX
+        paths. When enabled, DIO2 goes high when the chip is
+        transmitting.
+
+    dio3-tcxo-voltage:
+      type: int
+      required: false
+      description: |
+        TCXO supply voltage controlled by DIO3 if present.
+
+        See constants in dt-bindings/lora/sx126x.h.
+
+    tcxo-power-startup-delay-ms:
+      type: int
+      required: false
+      description: |
+        Startup delay to let the TCXO stabilize after TCXO power on.

include/dt-bindings/lora/sx126x.h

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+/*
+ * Copyright (c) 2020 Andreas Sandberg
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#ifndef ZEPHYR_INCLUDE_DT_BINDINGS_LORA_SX126X_H_
+#define ZEPHYR_INCLUDE_DT_BINDINGS_LORA_SX126X_H_
+
+#define SX126X_DIO3_TCXO_1V6	0x00
+#define SX126X_DIO3_TCXO_1V7	0x01
+#define SX126X_DIO3_TCXO_1V8	0x02
+#define SX126X_DIO3_TCXO_2V2	0x03
+#define SX126X_DIO3_TCXO_2V4	0x04
+#define SX126X_DIO3_TCXO_2V7	0x05
+#define SX126X_DIO3_TCXO_3V0	0x06
+#define SX126X_DIO3_TCXO_3V3	0x07
+
+#endif /* ZEPHYR_INCLUDE_DT_BINDINGS_LORA_SX126X_H_ */