Make ScreenUndimDetector only trigger on default display group

When only a non-default display group should be awake, the
ScreenUndimDetector was keeping the default display awake because it
wasn't looking at the display group id for the dim->bright transitions
that it watches.

Bug: 195266040
Test: atest ScreenUndimDetectorTest
Change-Id: I0900b3754913d859694e64ebec89529eeebf7ecd
4 files changed