drivers: rtc: stm32: Fixes RTC issues related to device runtime pm

When device runtime pm is enabled, Backup Domain protection is active
most of the time. RTC driver need this protection to be disabled in
order to set the time or calibration. This fix disable the protection in
set time and set calibration functions.

Fixes: 62843
Signed-off-by: Petr Hlineny <development@hlineny.cz>