Bluetooth: Classic: SCO: Add SCO conn connected/disconnected cb

Add two functions to register/unregister SCO conn connected/
disconnected callback.

Add macro BT_SCO_CONN_CB_DEFINE to defined static SCO connect callback.
Define section `bt_sco_conn_cb` to ROM.

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