AlwaysOnDisplay: let the maintainer disable or enable it

* AOD is a nice addition that will work well in devices with OLED displays,
  causing high battery drain in other display panels.

* Give the maintainer the ability to enable or disable it with a device overlay:
    config_enableDozeAlwaysOn
  False by default.

Change-Id: I41d88f8bf1216e337385e669e5a249a0f0cdc882
3 files changed