[SurfaceFlinger] Don't touch hw vsync in DEFAULT RR with kernel timeout

As a power optimization, hw vsync shouldn't be enabled when the kernel
timer resets if the display is going to run at 60hz anyways.

Bug: 136197211
Test: systrace when scrolling at peak refresh rate of 60hz.
Change-Id: Ic7df3e7b735f79b183cdd91f770de83082e491b4