Fix issues in GenericPlayer destruction

Fix issues in GenericPlayer destruction

Added a preDestroy() mechanism for the subclasses of
 GenericPlayer.
Added a lock around the update and use of the callback
 GenericPlayer is using for notifications to the
 OpenSL ES framework. This prevents notifications after
 the GenericPlayer is flagged for destruction.
Added a lock to protect the update of the audio source
 running state, so it doesn't get used after the
 AudioSfDecoder is flagged for destruction.
Before stopping the audio source of an AudioSfDecoder
 object, release the code buffer if necessary, to
 ensure proper teardown of the audio source (OMXCodec)

Change-Id: I6cf08d169a6da622552dda5101dbc61e663ce6aa