soc: stm32l4: Register soc log

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

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>

soc/arm/st_stm32/stm32l4/soc.c

@@ -14,6 +14,11 @@
 #include <init.h>
 #include <arch/cpu.h>
 #include <arch/arm/aarch32/cortex_m/cmsis.h>
+#include <logging/log.h>
+
+#define LOG_LEVEL CONFIG_SOC_LOG_LEVEL
+LOG_MODULE_REGISTER(soc);
+
 
 /**
  * @brief Perform basic hardware initialization at boot.