audio spatializer: monitor screen sensor only when needed

Only monitor the screen sensor when the head sensor must also
be monitored:
    - spatialization is enabled
    - head tracking is requested
    - a head pose sensor is registered
    - tracks are active on the spatializer output

Also remove excessive verbose log.

Bug: 224623509
Test: boot and check sensors
Change-Id: Icf0e4f69d3d342048decb127c23bf79ff196b8d4