power.stats: Add power.stats HIDL interface

Initial commit defines APIS to collect on-device
power-related data.

BUG: 117424656
BUG: 111185513
Test: Compilation and device boot
Change-Id: I6e3153c9fcd2d67e4a566a4621d7aa4c01da7636
(cherry picked from commit f91dcb5b)
Merged-In: I6e3153c9fcd2d67e4a566a4621d7aa4c01da7636