drivers: entropy nRF5x: hide the driver on non-nRF boards
drivers: entropy nRF5x: hide the driver on non-nRF boards

The nRF5x entropy driver does not depends on SOC_FAMILY_NRF is therefore
visible and selectable non-nRF5x SoCs. Fix that.

Signed-off-by: Aurelien Jarno <bceb368e7f2cb351af47298f32034f0587bbe4a6@aurel32.net>

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