brightness: dream-screen-on allows auto-brightness regardless offload

If dream-screen-on display request is made, allow auto-brightness when
the config allows and ignore displayoffload's decision.

Flag: EXEMPT. urgent change
Test: DisplayBrightnessStrategySelectorTest
Bug: 408278921
Change-Id: I6ed317b85dd9e50a487df9edd5de832dd08d27ea