AudioService: Fix cross deadlock with AudioDeviceBroker

Avoid VolumeStreamState calling back into AudioDeviceBroker
while locked on class mutex by caching Avrcp supported state in
AudioService.

Bug: 159672626
Test: repro steps in bug
Test: A2DP playback, routing and volume manual regression
Change-Id: I2a084cf9878ea7d79ad53aa57a13cd2875f42e93