Migrate to PowerWhitelistManager.

In preparation for DeviceIdle mainlining, we have to define stable APIs
for other modules and the rest of the system to use. This migrates to
the stable PowerWhitelistManager API.

Bug: 142420609
Bug: 144864180
Test: Android builds
Change-Id: I599847a8e07732318e61c77c1c5f084df57eca95