SF: enable VSyncReactor

Enable VSyncReactor timing system. This is a vsync timing system
intended to work with VRR, multiple fixed rates, and typical fixed  rate
devices.

System can be disabled with
setprop debug.sf.vsync_reactor 0; stop; start

Test: go/dispsync2-checks
Fixes: 140302863

Change-Id: I46bb8d55604136cc0eb8b249e465d6ae5470c3f3