Need to make sure smu buffers are pinned on resume.  This
matches what Fiji does.

Cc: stable@vger.kernel.org
Reviewed-by: NJunwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NKen Wang <Qingqing.Wang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>