drm/kms: allow drm_mode_group with no objects

Sometimes we could be controlling a device (such as an NVIDIA Tesla) that
has no crtcs/encoders/connectors.

One could argue that the driver should unset DRIVER_MODESET in this case,
but that changes a whole heap of the DRM's other behaviours, and it's much
easier to just be a modesetting driver without any outputs.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -886,9 +886,6 @@ int drm_mode_group_init(struct drm_device *dev, struct drm_mode_group *group)
 	total_objects += dev->mode_config.num_connector;
 	total_objects += dev->mode_config.num_encoder;
 
-	if (total_objects == 0)
-		return -EINVAL;
-
 	group->id_list = kzalloc(total_objects * sizeof(uint32_t), GFP_KERNEL);
 	if (!group->id_list)
 		return -ENOMEM;