drm: Register connector instead of calling register_connector callback

drm: Register connector instead of calling register_connector callback

drm_dp_mst_topology_mgr_cbs.register_connector callbacks are literally
identical amongst every driver and don't do anything other than
calling drm_connector_register(). Hence call drm_connector_register()
directly instead of a callback.

This is the preparatory step for removing the
drm_dp_mst_topology_mgr_cbs.register_connector callback hook.

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Suggested-by: Emil Velikov <emil.velikov@collabora.com>
Suggested-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200307083023.76498-2-pankaj.laxminarayan.bharadiya@intel.com
Reviewed-by: Lyude Paul <lyude@redhat.com>