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/t1000-e/T1000eBoard.h

@@ -4,7 +4,7 @@
 #include <Arduino.h>
 #include <helpers/NRF52Board.h>
 
-class T1000eBoard : public NRF52Board {
+class T1000eBoard : public NRF52BoardDCDC {
 protected:
   uint8_t btn_prev_state;