Allow double tap power to trigger camera during device is sleeping

In previous patch (ag/14791880), we fixed double tap power to launch
camera by returning the 'MaxMultiPressPowerCount' value, that would
tell the single key detector to detect a single tap or multi taps by
the timeout (MULTI_PRESS_TIMEOUT=300ms), that would defer
the screen off action cause user feel the suspend response time is
worse than before.

This CL would allow the action of triggering camera by double tap when
device is going to sleep started in first tap, then it could wake the
device when receive 'screenTurnedOff'.

It would also fix the single key detector that process the power key
for single tap and multi taps and make sure that are runing at policy
thread.

Bug: 191214622
Test: manual with the combinations of screen on/off, aod, security
keyguard, double tap/single tap power.

Change-Id: I6ec73818adbd4eff91500460df7337fdf61ac08b