drm/amd/display: add S/G support for Renoir

S/G (scatter/gather) display support for display
buffers in system memory.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>