audio policy: add Spatializer effect control

Add APIs to discover support for audio spatialization function and control a
spatializer output mixer and effect creation to Audio Policy Service.

When supported, a system service can retrieve a ISpatializer
interface to query supported features and set a spatialization mode.

When spatialization is enabled, the corresponding specialized output mixer is
created and the effect applied.

The audio policy manager will attach clients which audio attributes and
format qualifying for spatialization to the specialized output mixer.

Bug: 188502620
Test: make

Change-Id: Ie2734fb9bb3ef9b945431c6c9bd110b1434a79cd
Merged-In: Ie2734fb9bb3ef9b945431c6c9bd110b1434a79cd