Revert "Revert "SurfaceFlinger: give SF its own vsync phase""

This reverts commit 4b940301de8dd8b762a80855eeec212d28d05af5.
SurfaceFlinger: Enable Vsync trace for SF Composition

Enable traces to show s/w vsync which is used for composition
by surfaceflinger, this helps in identifying the start of
composition cycle in systrace

Change-Id: Id892ca03bacd9f0cfe5ca2c3f8bb5aa892b37231
Merge remote-tracking branch 'vanir/kk44' into HEAD