ext: gecko: Add workaround in em_emu.h
ext: gecko: Add workaround in em_emu.h

For the EFM32PG12B, the define _EMU_EM23PERNORETAINCTRL_VDAC0DIS_MASK
is not availabe. This commit guards its usage with ifdefs.
This might be a bug in the gecko SDK or some version incompatibility
in the used files.

Signed-off-by: Christian Taedcke <1d7d3458c4d94e1013a9872dbd5fe0865ba6a124@taedcke.com>

Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,explora26/zephyr,finikorg/zephyr,ldts/zephyr,ldts/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,Vudentz/zephyr,nashif/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,explora26/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,punitvara/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,explora26/zephyr,nashif/zephyr