commit a3ed353c upstream.

fixes S3 issue with IOMMU + S/G  enabled @ 64M VRAM.
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>