android/handsfree: Factor out HFP AG enable code
android/handsfree: Factor out HFP AG enable code

This is in preparation for support to not enable HFP AG when
initializing HAL.

ComputeCycles/bluez,pkarasev3/bluez,pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,ComputeCycles/bluez,ComputeCycles/bluez,ComputeCycles/bluez,mapfau/bluez,silent-snowman/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez