soc: stm32l4: Register soc log
soc: stm32l4: Register soc log

There are places using log with domain soc without this it being
registered.

Signed-off-by: Flavio Ceolin <979b9165500b0741b9d0500e2efd74fc1547bff7@intel.com>

finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr