libhwcomposer: Synchronize Uevent and Composition threads

When Uevent thread needs to wait for composition cycle to be completed
It should be signaled by the Condition variable rather than waiting
based on 2 vsync cycles of sleep, which is not guaranteed.

Change-Id: I5a868c75393d201791e417f5450a8164c6025d68
Revert "overlay: Add tolerance to downscale factor"

This reverts commit c2be636a6c49b760592e8ff50141204c377ed414.

Change-Id: I2b850a8a8d5e11736780a92fd3a8421ace0e2542