Floss: expose DBus method to allow AudioState query

Upon the audio stack sending StartAudioRequest, this method will be used
to periodically query the AudioState until it has transitioned to the
'Started' state so that the audio stack can start sending data over.

Bug: 236769419
Tag: #floss
Test: Build and verify DBus method exposed
Change-Id: Ia954ed2cee02565acf24e1d72c54f02c7658749b