rtc: pcf2127: set RTC_FEATURE_ALARM_RES_2S

The PCF2127 doesn't support UIE because setting an alarm to fire every
second confuses the chip and the fastest we can go is an alarm every 2
seconds.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220309162301.61679-11-alexandre.belloni@bootlin.com