AudioService: optimize service creation

  Delay a number of stream and volume initialization steps
to after the creation of the service to reduce system_server
initialization time.
  Clean-up:
- class StreamVolumeCommand should be static, it doesn't access
  AudioService resources
- make mRmtSbmxFullVolDeathHandlers and mAudioServerStateListeners
  final as they are never modified after creation, and used for
  synchronization.

Bug: 164516518
Test: atest AudioManagerTest
Change-Id: I9afd7989793f20480b3059ee80ab403c5e4ee969