Bluetooth: A2DP: implement reconfig and optimize codes

Implement the bt_a2dp_stream_reconfig: Modify reconfig_req callback to
pass codec_cfg to application. Remove reconfig_rsp callback,
config_rsp is used. Remove reconfigured callback,
configured callback is used.

move the status to common struct bt_avdtp_req,
use same bt_avdtp_ctrl_params to process control-like avdtp
cmds (start, open etc), use the same a2dp_ctrl_ind to process
control-like cmds (start, open etc), use the same
bt_a2dp_ctrl_cb to process control-like cmds (start, open etc),
use the same bt_avdtp_ctrl to process control-like cmds
(start, open etc), optimize getting a2dp conn by index,
use sem to replace mutex and optimze the lock codes to be
based on context/instance.

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