Enable AutoBrightness per display

Allow each display to specify whether autobrightness should be used or
not.

Bug: 179021925
Test: atest BrightnessTrackerTest
Test: check both displays use autobrightness;
      adb shell dumpsys display | grep "mAutoBrightnessAvailable\|mUseSoftwareAutoBrightnessConfig"

Change-Id: I7e0b8442c0724da8f9a9b0c6b455f558a42f40c9
Merged-In: I7e0b8442c0724da8f9a9b0c6b455f558a42f40c9