drivers/clock_control: stm32wl set cpu2 prescaler only for STM32WL5X
drivers/clock_control: stm32wl set cpu2 prescaler only for STM32WL5X

To support single core stm32wlex series, cpu2 prescaler is set
only on dual core soc variants.

Signed-off-by: Thomas Stranger <289fb7da2789c69f49f06a4b4e006530cf91f1de@outlook.com>

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