Added default temperature from ESP32 MCU and NRF52 MCU

Added NRF52Board.h and NRF52Board.cpp
Modified NRF52 variants to extend from NRF52Board to share common feature

variants/nano_g2_ultra/nano-g2.h

@@ -4,6 +4,7 @@
 
 #include <Arduino.h>
 #include <MeshCore.h>
+#include <helpers/NRF52Board.h>
 
 // LoRa radio module pins
 #define P_LORA_DIO_1             (32 + 10)
@@ -34,7 +35,7 @@
 #define PIN_VBAT_READ            (0 + 2)
 #define REAL_VBAT_MV_PER_LSB     (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
 
-class NanoG2Ultra : public mesh::MainBoard {
+class NanoG2Ultra : public NRF52Board {
 protected:
   uint8_t startup_reason;