Spatializer: update getSupportedHeadTrackingModes()

ISpatializer.getSupportedHeadTrackingModes() result is now
independent from actually connected sensors and reflects the
capabilities when sensors are available.
Also do not report screen relative mode as this is currently not
supported by the head tracking library implementation.

Bug: 231252067
Test: make
Change-Id: I0b8be86b5c720024c342911accc580c1aba4f82e