variants: Ikoka NRF: Use DC/DC regulator

The Ikoka boards are based on the Xioa NRF52840 module which is known
to have the LC circuit for the internal DC/DC regulator to be
available. Enable it to save power.

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

variants/ikoka_handheld_nrf/IkokaNrf52Board.h

@@ -6,7 +6,7 @@
 
 #ifdef IKOKA_NRF52
 
-class IkokaNrf52Board : public NRF52BoardOTA {
+class IkokaNrf52Board : public NRF52BoardDCDC, public NRF52BoardOTA {
 public:
   IkokaNrf52Board() : NRF52BoardOTA("XIAO_NRF52_OTA") {}
   void begin();