libhwc2.1: use vblank while waiting peak refresh rate for LHBM

Using fixed vsync period may end up unnecessary waiting time
while waiting peak refresh rate for LHBM. Use vblank instead
to avoid this situation.

Bug: 237835586
Test: capture a trace to check the timing
Change-Id: Iecb030172b58fa46c5a37658186b5c52e467cc96