rtc: tps65910: remove tps65910_rtc_ops_noirq

Clear RTC_FEATURE_ALARM to signal that alarms are not 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/20210110231752.1418816-18-alexandre.belloni@bootlin.com