audio: Set correct priority for the SPATIALIZER stream thread

To align with the framework, the thread serving SPATIALIZER
stream I/O must use SCHED_FIFO and realtime priority.
The latter can be set via `audio.spatializer.priority`
property.

Bug: 321233946
Test: adb shell ps -Tl -p <HAL PID>
Change-Id: I80107c9aa7d86cbfc2f79c2ad05959fc9f7913f7