Bluetooth: A2DP: Implement the a2dp and avdtp

implement a2dp.c and avdtp.c
add a2dp related Kconfig:
BT_AVDTP_RTP_VERSION, BT_A2DP_SOURCE and BT_A2DP_SINK
a2dp_codec_sbc.c/h are used to provide some APIs to get
A2DP SBC codec information. (like: channel num).

Signed-off-by: Mark Wang <yichang.wang@nxp.com>