Hold wakelock while there are active power key related timers

There is a state machine for separating short, long and double
power key presses. The detection logic uses timers, and we need
to ensure the device does not fall back to suspend while the
timers are active.

[mce] Hold wakelock while there are active power key related timers
Merge pull request #124 from spiiroin/powerkey_wakelock

Hold wakelock while there are active power key related timers