drivers: entropy: Clock activation is missing on stm32l4
drivers: entropy: Clock activation is missing on stm32l4

On STM32L4 SoCs RNG is clocked by 48MHz domain.
Hence, besides clock activation, it requires 48M
domain to be enabled.

Tested on:
*nucleo_l476rg
*stm32l476g_disco
*disco_l475_iot1

Signed-off-by: Erwan Gouriou <de4d967452b83bb0e37525652734e7d9163b6a4c@linaro.org>

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