drm/amdgpu: disable uvd pg on Tonga.

it does not work with GPU pass through if the VM
is not cleanly shutdown leading to a hang when the
modules is reloaded.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org