Improve the boot animation fix

- do not use mPendingDeviceState as it's used to wait for the displays to turn off
- don't sleep on the first device state transition

Bug: 193821864
Bug: 265088477
Test: atest LogicalDisplayMapperTest
Test: atest PowerTest#power2RockBottomCheckTest
Change-Id: Ia258c0556948c790d073adec5a8b4ef6888dddc4