PowerUI access to thermalservice

Allow PowerUI / platform_app to use thermalservice for receiving
notifications of thermal events.

Bug: 66698613
Test: PowerNotificationWarningsTest, PowerUITest,
      manual: marlin and <redacted> with artificially low temperature
      threshold and logcat debugging messages
Change-Id: I5428bd5f99424f83ef72d981afaf769bdcd03629
Merged-In: I5428bd5f99424f83ef72d981afaf769bdcd03629