rtc: qpnp-rtc: Read ALARM_EN and update to alarm enabled status

ALARM_EN status would be retained in PMIC register after device shutdown
if poweron_alarm is enabled. so read it to make sure the driver has
consistent value with the register status.

CRs-Fixed: 2070501
Change-Id: Iee0a19ba5126265b36a353c1d1b249d09185564a
Signed-off-by: Mao Jinlong <c_jmao@codeaurora.org>