WaitForNegativeProximity stopped with power button.

If the device is in a state where it is waiting for negative
proximity event to turn the screen back on (as with phone calls),
this CL makes it so that power button will also turn the screen
back on, even if proximity is still positive.

Test: make phone call, cover prox, end call. Previously power button
      had no effect in this state, now it turns the screen back on.
Bug: 190459207
Change-Id: I3ce33fe81e5ee0c0652517a8ce46632519ba73c6