drm/bridge: tfp410: Allow operation without drm_connector

The tfp410 driver can operate as part of a pipeline where the
drm_connector is created by the display controller. Enable this mode of
operation by skipping creation of a drm_connector internally.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226112514.12455-20-laurent.pinchart@ideasonboard.com