SurfaceFlinger: always turn HWVsync off when display is off

Maintain a state in SF about what is the latest HWVsync state in HWC
and what it should be. Apply the desired state when screen turns on and
always disabled HWVsync when the display is off.

Test: display power on/off
Bug: 134965007
Change-Id: I9c23d09ea2e32efa0b1f30a3999a08d15d7f35a6