rtc: pcf2127: remove pcf2127_rtc_alrm_ops

Move the alarm callbacks in pcf2127_rtc_ops and use RTC_FEATURE_ALARM to
signal to the core whether alarms are available instead of having a
supplementary struct rtc_class_ops without alarm callbacks.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210110231752.1418816-8-alexandre.belloni@bootlin.com