Fix Power Menu vanish when display size is Large

- Break the power button alignment when power menu height larger then screen height,
remove power menu padding and set gravity to center vertical within the screen.

Test: Manually, set display size or font size to large, larger or largest & check
power menu should be center vertical/horizontal when power menu height
larger then screen height.
Bug: 110761858

Change-Id: Ice7f816a30fa0f565a9098b3d6d5989aca9a4e5b