spatializer: disable head tracker sensor when not neeeded

Only enabled the head tracker sensor when the following conditions
are met:
- Spatialization is enabled
- Head tracking desired mode is not static
- A valid head tracking sensor is set
- At least one audio track is active on the spatializer mixer

Bug: 218273231
Test: manual test with uhid-sample sensor simulator

Change-Id: Ie3acd27f4387a9192f907d99a6798a1d8224df12