soc: stm32f4: Fix PM dependency

COUNTER_RTC_STM32_SUBSECONDS depends on DT_HAS_ST_STM32_RTC_ENABLED.

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

soc/arm/st_stm32/stm32f4/Kconfig.defconfig.series

@@ -19,6 +19,6 @@ config TASK_WDT_HW_FALLBACK_DELAY
 
 config PM
 	select COUNTER
-	select COUNTER_RTC_STM32_SUBSECONDS
+	select COUNTER_RTC_STM32_SUBSECONDS if DT_HAS_ST_STM32_RTC_ENABLED
 
 endif # SOC_SERIES_STM32F4X