Add VTS tests for PowerStats HAL 2.0

Right now these VTS tests only check for successful return status since
this HAL only contains a stub implementation at the moment. These tests
will be updated as this HAL implementation is completed.

Bug: 165345767
Test: atest VtsHalPowerStatsTargetTest
Change-Id: I3a6a4a333ee743fac4eba8ae225d5d1c9ffff32e