rtc: ab-eoz9: make use of RTC_FEATURE_ALARM

Move the alarm callbacks in rtc_ops and use RTC_FEATURE_ALARM to notify
the core whether alarm capabilities are available or not.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210408024028.3526564-4-liambeguin@gmail.com