drm/amd/display: disable S/G display on DCN 2.1.0

Causes flickering or white screens in some configurations.
Disable it for now until we can fix the issue.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2352
Cc: roman.li@amd.com
Cc: yifan1.zhang@amd.com
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>