On modern gpus, GTT (system memory) works as well here, and this may
also be a workaround for platforms which cannot map vram correctly.
Signed-off-by: Nchenli <chenli@uniontech.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>