introduce shutdownPeripherals in NRF52Board to prepare for shutdown

src/helpers/NRF52Board.cpp

@@ -298,7 +298,7 @@ float NRF52Board::getMCUTemperature() {
   return temp * 0.25f; // Convert to *C
 }
 
-void NRF52Board::powerOff() {
+void NRF52Board::shutdownPeripherals() {
   // Power off the display if any
 #ifdef DISPLAY_CLASS
   display.turnOff();
@@ -318,6 +318,10 @@ void NRF52Board::powerOff() {
   // Flush serial buffers
   Serial.flush();
   delay(100);
+}
+
+void NRF52Board::powerOff() {
+  shutdownPeripherals();
 
   // Enter SYSTEMOFF
   uint8_t sd_enabled = 0;

src/helpers/NRF52Board.h

@@ -50,6 +50,7 @@ public:
   virtual uint8_t getStartupReason() const override { return startup_reason; }
   virtual float getMCUTemperature() override;
   virtual void reboot() override { NVIC_SystemReset(); }
+  virtual void shutdownPeripherals();
   virtual void powerOff() override;
   virtual bool getBootloaderVersion(char* version, size_t max_len) override;
   virtual bool startOTAUpdate(const char *id, char reply[]) override;

variants/lilygo_techo/TechoBoard.h

@@ -23,8 +23,8 @@ public:
     return "LilyGo T-Echo";
   }
 
-  void powerOff() override {
-    NRF52Board::powerOff();
+  void shutdownPeripherals() override {
+    NRF52Board::shutdownPeripherals();
     #ifdef LED_RED
     digitalWrite(LED_RED, HIGH);
     #endif