hfp_ag: Remove emulator from modem when disconnect
hfp_ag: Add Audio Card to emulator when connect
hfp_ag: Set Audio Card's local and remote address
hfp_ag: Add a card driver for HFP 1.6

This is just the skeleton of a Handsfree Audio Card for the HF side of
HFP 1.6.
hfp_ag: Extract Version from fd dictionary
hfp_ag: Pass version to card registration
hfp_ag: Pass emulator to card creation

This way we can access the emulator in the card's probe function.
hfp_ag: Add callback to handle AT+BAC from HF
hfp_ag: Add callback to handle AT+BCC from HF

This commit registers a callback to be executed when the HFP AG 1.6
receives a AT+BCC command.
hfp_ag: Implement callback that handles AT+BAC
hfp_ag: Implement callback that handles AT+BCC