audio: Add API to handle active device change

Add API to handle active device change based on
whether we are switching between:
null to 'X'
'X' to 'Y'
'X' to null
This API must be called from A2dpService to update
active device.
Same API also caters to device config change on
an already connected A2DP device.

Bug: 111812273
Test: make
Change-Id: I9f28092934ee611fbc2cd7c81447b4ed22288ac9
3 files changed