drm: add register and unregister functions for connectors

Introduce generic functions to register and unregister connectors. This
provides a common place to add and remove associated user space
interfaces.

Signed-off-by: Thomas Wood <thomas.wood@intel.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dvo.c

@@ -558,7 +558,7 @@ void intel_dvo_init(struct drm_device *dev)
 			intel_dvo->panel_wants_dither = true;
 		}
 
-		drm_sysfs_connector_add(connector);
+		drm_connector_register(connector);
 		return;
 	}