DispSync: workaround HH hardware vsync issue

The HWC of HH seems to have a bug where it fails to generate vsync events upon
the first eventControl call to turn on HWC_EVENT_VSYNC.

The workaround is for DispSync to detect when it has received no resync samples
after many presents, and return false so that SF will disable HW vsync and
re-enable it in the next present. This gets the HWC of HH out of the bad state.

Bug:25845510
TEST=reboot HH then immediately capture systrace while scrolling all apps

Change-Id: Ie034c113d94ea53068eef75b8eac39a32788666a