drm: WARN_ON if a modeset driver uses legacy suspend/resume helpers

Legacy s/r hooks are only used for shadow-attaching drivers, warn
when a KMS driver tries to use them.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_drv.c

@@ -566,6 +566,8 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 		ret = drm_minor_alloc(dev, DRM_MINOR_CONTROL);
 		if (ret)
 			goto err_minors;
+
+		WARN_ON(driver->suspend || driver->resume);
 	}
 
 	if (drm_core_check_feature(dev, DRIVER_RENDER)) {