DMD: Support 90hz only in the refresh rate zone

Also allow DeviceConfig to change the zone behavior
to 60 Hz only.

Change BrightObserver priority to be the lowest so application
request won't be overriden by BrightnessObserver

Bug: 139487676
Change-Id: I959550350c1ea72f764984226350ebc6e7de591c
4 files changed