Deduplicate DC/DC regulator enable for NRF52 boards

Some NRF52 boards are able to use the internal power-efficient DC/DC
regulator. Add a new class that can be inherited by board classes to
enable this feature and reduce the power consumption.

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

variants/xiao_nrf52/XiaoNrf52Board.cpp

@@ -21,16 +21,7 @@ static void disconnect_callback(uint16_t conn_handle, uint8_t reason) {
 }
 
 void XiaoNrf52Board::begin() {
-  NRF52Board::begin();
-
-  // Enable DC/DC converter for improved power efficiency
-  uint8_t sd_enabled = 0;
-  sd_softdevice_is_enabled(&sd_enabled);
-  if (sd_enabled) {
-    sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE);
-  } else {
-    NRF_POWER->DCDCEN = 1;
-  }
+  NRF52BoardDCDC::begin();
 
   pinMode(PIN_VBAT, INPUT);
   pinMode(VBAT_ENABLE, OUTPUT);

variants/xiao_nrf52/XiaoNrf52Board.h

@@ -6,7 +6,7 @@
 
 #ifdef XIAO_NRF52
 
-class XiaoNrf52Board : public NRF52Board {
+class XiaoNrf52Board : public NRF52BoardDCDC {
 public:
   void begin();