drivers: rtc: smartbond: Update RTC driver

This commit should fix the followings:
1.  When an alarm event is initialized, the driver should only
    consume the valid alarm fields, based on the given mask.
    Otherwise, the driver should use default valid subfield
    values.
2.  Setting an alarm event should not return with error code
    if the timer and/or calendar counters have yet to be
    initialized, explicitly. Instead, a log warning should be
    issued.

Signed-off-by: Ioannis Karachalios <ioannis.karachalios.px@renesas.com>