Revert "rtc: alarm: Change wake-up source"

This reverts commit dad42958.

Power off alarm is not set through alarmtimer now and lpm_wake_up
doesn't work on latest msm platform. So revert this commit.

CRs-Fixed: 2132189
Change-Id: I03ca0c2f046f0c9d42823b2e0b46b68e3b39352b
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>