audioservice: system audio control in master volume mode

Volume control in master mode should be transformed to
CEC commands if system audio is activated to delegate
the control to the connected AV receiver.

Refactored to use the interface to CEC service for
both master and stream type volume control.

Bug: 18560079

Change-Id: I2aefdc94a1bc3091c14fab849f899a0dc37c47bc