power: This HAL is only for Google devices

Change-Id: If50f9c72f6a336200bd1e3a4c5d1a0b6b54e0533
power: Additional guards

Change-Id: I67f8ffc55e734ada251e42b4ed50bc038f63b3d2
power: Deal with TARGET_POWERHAL_VARIANT

Change-Id: I7d68066b17ce54866ae354669a7b05029d7b12f7