AudioService: surround info has its own lock

Make utility methods (conversions, validity check) static, no lock
or annotation needed.

Continue moving independent information in AudioService under
their own locks to prevent lock nesting:
surround format information is guarded by mSurroundLock
Affects:
  mEncodedSurroundMode
  mEnabledSurroundFormats
  mSurroundModeChanged
  setting for ENCODED_SURROUND_OUTPUT_ENABLED_FORMATS

Bug: 287066735
Flag: EXEMPT code health
Test: atest AudioManagerTest
Test: m -j RUN_ERROR_PRONE=true services | tee error_prone_services.txt

Change-Id: Id10acd8e5479afc4c97286236f33b7c27df9049a