Improve auto-brightness handling

- Add a setting to control the auto-brightness algorithm responsitivity
- Make the algorithm react much faster when the ambient brightness
  increases quickly, e.g. when receiving a call in bright sunlight.

Change-Id: Ic608901c476609dde69cae982228c09567140a83

Conflicts:
	services/java/com/android/server/power/PowerManagerService.java
power: Add panel auto-brightness configuration

 * Some panel hardware requires that we twiddle some knobs in sysfs to
   enable proper display calibration (gamma, etc) when auto-brightness
   is enabled. Add a configuration value to handle this.

Change-Id: I3c793c3520fc6f9a18d5a3abf1fe0df803c5e580

Conflicts:
	core/res/res/values/config.xml
	services/java/com/android/server/power/AutoBrightnessHandler.java
	services/java/com/android/server/power/PowerManagerService.java