Spatializer: set spatializer threads to RT priority 1

In order to ensure glitch-free low latency head tracking,
set the following threads to the lowest RT priority:
  1) AudioFlinger SpatializerThread
  2) Audio HW service StreamOut Spatializer writer worker thread
  3) Audio HW service AudioEffect Spatializer worker thread

The RT priority level is configurable by property as follows:

// Enable real time priority (higher is better) -
// we allow values from 1 - 3, defaults to 1.
// If the value is outside that range,
// the highest non-realtime priority is used.
$ adb shell setprop audio.spatializer.priority 3

// After setting the property, kill audioserver to reinitialize.
// This can occur while playback is ongoing.
$ adb shell pkill audioserver

Test: as above
Bug: 253276925
Change-Id: Ic9008c2ed5856410cae7a89fa9ba0533c20d7b10