Update power up brightness when starting display state transition

The power up brightness was evaluated too late and caused jumps in
brightness during unblanking. Possible went unnoticed until changes
to ambient light sensor power up were made to accommodate the proximity
based lpm display states.

[mce] Update power up brightness when starting display state transition. Fixes JB#20590
Merge pull request #183 from spiiroin/unblank_brightness

Update power up brightness when starting display state transition