dfc: hold wakelock while powersave timer is running

Powersave alarm timer could fail and delay suspend for 2 seconds
if the timer expires in 2 seconds. Change to hold a wakelock for
the actual duration of the timer so the suspend can be triggered
after timer expiration without delay.

Change-Id: Icc3cb835d4e174955e128c5a0c80198513213b2d
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>