[Why]
To send sdp message immediately from a single slot.

[How]
Modify the generic SDP message interface, and use GSP4 to send immediate
sdp message.
Signed-off-by: NLeo (Hanghong) Ma <hanghong.ma@amd.com>
Reviewed-by: NHarry Wentland <Harry.Wentland@amd.com>
Acked-by: NBhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>