Request power state updates for individual DisplayGroups

Update PowerManagerService to track and update the power state of
DisplayGroups individually.

This allows for different Displays to be on or off instead of needing to
all share the same power state.

Bug: 138328918
Test: atest FrameworksServicesTests:PowerManagerServiceTest
Change-Id: Ia32039415863ba745c7de2fba55bf25e68de4d15