SurfaceFlinger: add display power state timer

Coming out of DOZE mode might result in unstable HWVsync which may
confuse FPS detection logic to set the desired refresh rate.
To mitigate that, this change introduces a new timer that will provide
a grace period when coming out of DOZE while in this grace period refresh
rate will stay in PERFORMANCE.

Test: Toggle DOZE by hitting the power button and collect systrace
Bug: 135550670
Change-Id: Ib8ec3c9550336d691dd3868405d20b98aa983302
(cherry picked from commit 24363178)
Merged-In: Ib8ec3c9550336d691dd3868405d20b98aa983302