SF: Toggle VSYNC in EventThread with state machine

This CL simplifies the logic to enable and disable VSYNC in the
EventThread loop.

Bug: 74619554
Test: libsurfaceflinger_unittest
Test: dumpsys SurfaceFlinger --vsync

Change-Id: I7637fcf1982d60cfced5dae68c74556f0ee67a0f
3 files changed