SpatializerHelper: head tracking init / dump

When initializing the sensors, also set the headtracking mode
to the desired mode, which defaults to RELATIVE_WORLD.

When changing the desired tracking mode, compare against
the current tracking mode instead of the previous
desired mode.

Dump state information from AudioService dump.

Bug: 210803914
Test: atest SpatializerTest#testHeadTrackingListener
Change-Id: I5144d3218223f241cf047d00f843c518c1e617b8