Processing autobrightness mode in async

setAutomaticScreenBrightnessMode function is currently executed from the
display thread, while the automaitc brightness controller utilities
should only be accessed from the power thread. To achieve this, the
logic is now being executed via the handler event

Bug: 341026483
Test: atest DisplayPowerControllerTest
Change-Id: I0f228ee76119780dc278e37b7cf06738a3a9dee6