drm/amd/display: disable S/G display on DCN 3.1.5

commit e78cc6a4 upstream.

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

Bug: amd#2354


Cc: roman.li@amd.com
Cc: yifan1.zhang@amd.com
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 6.1.x
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>