drm/amd/display: Initialize GSP1 SDP header

[Why + How]
Initialize GSP1 SDP header for use in DMCUB FW.

Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>