Avrcp: call audioManager on non-Blocking thread

AudioManager has implemented setDeviceVolumeBehavior as a blocking call
In order to make sure we do not block Bluetooth, we need to make the
call in an async way.

Bug: 324420709
Flag: Exempt, mandatory fix to land unflaggable aosp/3009913
Test: atest pts-bot:AVRCP
Change-Id: Ibf1cf8602d15b9329c10f340f741737908ae9c11