Move power HAL interactions to PowerManagerService.

Move power HAL interactions to PowerManagerService.

This refactoring sets the stage for a follow-on change that
will make use additional functions of the power HAL.

Moved functionality from android.os.Power into PowerManagerService.
None of these functions make sense being called outside of the
system server.  Moving them to the PowerManagerService makes it
easier to ensure that the power HAL is initialized exactly once.

Similarly, moved ShutdownThread out of the policy package and into
the services package where it can tie into the PowerManagerService
as needed.

Bug: 6435382
Change-Id: I958241bb124fb4410d96f5d5eb00ed68d60b29e5