Audio : Spatializer : fix head tracking modes

Several fixes on head tracking mode reporting:
- Query and cache the supported modes at initialization time as those
do not change after that.
- Store the actual mode upon spatializer creation and when the mode
 update callback is received and use this value for the getter API.

Bug: 231252067
Test: atest SpatializerTest
Change-Id: I2fa76b84f709458d87904c88e522348023ee89b3