Make HVAC dep properties unavailable to get when power is off.

Previously HVAC properties are unavailable to set when hvac power is
off. This CL makes VHAL returns NOT_AVAILABLE for get as well. VHAL
will also generate property change event when the power is switched
on again.

Test: atest FakeVehicleHardwareTest
Bug: 262461830
Change-Id: I17ca8a4e48f3ff5854226a6a38a42220078073d5