A2DP SRC offload support

bluedroid changes to support A2DP SRC offload to BT FW.
add functionality to relay a2dp offload requests and responses
between AudioHAL & the BT vendor library.

Change-Id: Ie4e5992c48e95b0efb372a405e8537e4fd3ea071
Signed-off-by: Sridhar Vashist <svashist@motorola.com>

Conflicts:
	audio_a2dp_hw/audio_a2dp_hw.h
	bta/Android.mk
	bta/av/bta_av_aact.c
	btif/include/btif_media.h
	btif/src/btif_av.c
	btif/src/btif_media_task.c
	hci/Android.mk
	hci/src/vendor.c
	include/bt_target.h
	stack/include/l2c_api.h