gpu: drm: xylon: Fixed connector register/unregister functionality

Replaced drm_sysfs_connector_add() with drm_connector_register() and
drm_sysfs_connector_remove() with drm_connector_unregister().

Signed-off-by: Davor Joja <davorjoja@logicbricks.com>
Tested-by: Christian Kohn <christian.kohn@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>