60hz only when ambient or display brightness is low

Due to hardware limitation, flickers are seen when switching between 60
and 90hz at low display and ambient brightness. Force the display to stay
at 60hz when ambient and display brightness are low.

Bug: 136461712
Exempt-From-Owner-Approval: Santos is designated by Michael
Change-Id: I931288c46fc658e25b25249a160904b3e2dcfb94