Ensure Binder in-calls to UiModeManagerService are guarded.

Fixed a couple of problems where locks were not being taken or
where the calling identity was being clear deep in the call
stack whereas it should be cleared as close to the entry point
possible to ensure code correctness.

Bug: 7328545
Change-Id: I8ff646a772cd7f4025d5604bc35c6372c3d2428e