Use common NRF52 begin() and deduplicate() startup reason init

Use a common begin() method that can be called from derived classes
to contain the shared initialization code.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

variants/ikoka_handheld_nrf/IkokaNrf52Board.cpp

@@ -21,8 +21,7 @@ static void disconnect_callback(uint16_t conn_handle, uint8_t reason) {
 }
 
 void IkokaNrf52Board::begin() {
-  // for future use, sub-classes SHOULD call this from their begin()
-  startup_reason = BD_STARTUP_NORMAL;
+  NRF52Board::begin();
 
   // ensure we have pull ups on the screen i2c, this isn't always available
   // in hardware and it should only be 20k ohms. Disable the pullups if we

variants/ikoka_handheld_nrf/IkokaNrf52Board.h

@@ -7,12 +7,8 @@
 #ifdef IKOKA_NRF52
 
 class IkokaNrf52Board : public NRF52Board {
-protected:
-  uint8_t startup_reason;
-
 public:
   void begin();
-  uint8_t getStartupReason() const override { return startup_reason; }
 
 #if defined(P_LORA_TX_LED)
   void onBeforeTransmit() override {