Add support for Adafruit Feather RP2040 with RFM95. (#4451)

* Add support for Adafruit Feather RP2040 with RFM95.

* Update mesh.pb.h

dropping this change from the file generated by the protobuf

* Update mesh.pb.h

remove these reverting changes

* Update mesh.pb.h

oops, missed a comma

variants/feather_rp2040_rfm95/variant.h

@@ -0,0 +1,61 @@
+// #define RADIOLIB_CUSTOM_ARDUINO 1
+// #define RADIOLIB_TONE_UNSUPPORTED 1
+// #define RADIOLIB_SOFTWARE_SERIAL_UNSUPPORTED 1
+
+#define ARDUINO_ARCH_AVR
+
+// #define USE_SSD1306
+
+// #define USE_SH1106 1
+
+// default I2C pins:
+// SDA = 4
+// SCL = 5
+
+// Recommended pins for SerialModule:
+// txd = 8
+// rxd = 9
+
+#define EXT_NOTIFY_OUT 22
+#define BUTTON_PIN 7
+// #define BUTTON_NEED_PULLUP
+
+#define LED_PIN PIN_LED
+
+// #define BATTERY_PIN 26
+//  ratio of voltage divider = 3.0 (R17=200k, R18=100k)
+// #define ADC_MULTIPLIER 3.1 // 3.0 + a bit for being optimistic
+
+#define USE_RF95 // RFM95/SX127x
+
+#undef LORA_SCK
+#undef LORA_MISO
+#undef LORA_MOSI
+#undef LORA_CS
+
+// https://www.adafruit.com/product/5714
+// https://learn.adafruit.com/feather-rp2040-rfm95
+// https://learn.adafruit.com/assets/120283
+// https://learn.adafruit.com/assets/120813
+#define LORA_SCK 14  // 10 12P
+#define LORA_MISO 8  // 12 10P
+#define LORA_MOSI 15 // 11 11P
+#define LORA_CS 16   // 3 13P
+
+#define LORA_RESET 17 // 15 14P
+
+#define LORA_DIO0 21 // ?? 6P
+#define LORA_DIO1 22 // 20 7P
+#define LORA_DIO2 23 // 2 8P
+#define LORA_DIO3 19 // ?? 3P
+#define LORA_DIO4 20 // ?? 4P
+#define LORA_DIO5 18 // ?? 15P
+
+#ifdef USE_SX1262
+#define SX126X_CS LORA_CS
+#define SX126X_DIO1 LORA_DIO1
+#define SX126X_BUSY LORA_DIO2
+#define SX126X_RESET LORA_RESET
+#define SX126X_DIO2_AS_RF_SWITCH
+// #define SX126X_DIO3_TCXO_VOLTAGE 1.8
+#endif