Revert "drm/amd/display: enable S/G for RAVEN chip"

This reverts commit 1c425915.

S/G display is not stable with the IOMMU enabled on some
platforms.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=205523


Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org