spatialier: more head pose controller optimizations

Spatializer:
- do not suppress pose updates when actual head tracking mode is
  disabled
- remove redundant check on mode changed in onActualModeChangeMsg()
- do not wait for pose calculation when creating the head pose
  controller

SpatializerPoseController:
- fix potential race condition between mShouldExit and mShouldCalculate
- allow constuction without maxUpdatePeriod

Bug: 227740874
Test: Spatial audio playback with and without head pose sensor
Change-Id: I92fa5158ba7ffda564a021b03e81b6ff3d124351