variants: Heltec T114: Enable DC/DC regulator

According to the documentation and experiments on other boards using
NRF52 + SX1262 this reduces the power consumption significantly.

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

variants/heltec_t114/T114Board.cpp

@@ -21,6 +21,7 @@ static void disconnect_callback(uint16_t conn_handle, uint8_t reason) {
 void T114Board::begin() {
   // for future use, sub-classes SHOULD call this from their begin()
   startup_reason = BD_STARTUP_NORMAL;
+  NRF_POWER->DCDCEN = 1;
 
   pinMode(PIN_VBAT_READ, INPUT);