Keep automatic screen brightness monotonically increasing until screen is turned off.

This is an experimental change to avoid the light sensor screen fluctuation problem.
We only do this when undocked to since the lighting should be stable in the docked case
and since the dock keeps the screen on we need to be able to adjust the lighting.

Change-Id: I70afcc393f51f2679be8228d6cb993ddc07e5986
BUG: 2387223
Signed-off-by: Mike Lockwood <lockwood@android.com>