Bluetooth: Host: Add SCO Connect notify for HFP

Call bt_sco_server_register to register SCO
server. Manage the SCO connection request.
Get SCO connect/disconnect status via SCO
channel ops.

Notify the uppper layer of the SCO connection
status changes through bt_hfp_hf_cb::
sco_connected and bt_hfp_hf_cb::
sco_disconnected.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>