dfc: Use alarm timer to trigger powersave work

The timer in the delayed powersave work may not get fired at specified
interval during system suspend. The delay of the powersave work could
cause unexpected wakeups. Change to use alarm timer to trigger the
powersave work.

Change-Id: Ibd04c36e5f38988829c28684e8e9a9e6c2dbdfe9
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>