drm/bridge: tfp410: Replace manual connector handling with bridge

Now that a driver is available for display connectors, replace the
manual connector handling code with usage of the DRM bridge API. The
tfp410 driver doesn't deal with the display connector directly anymore,
but still delegates drm_connector operations to the next bridge. This
brings us one step closer to having the tfp410 driver handling the
TFP410 only.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.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/20200226112514.12455-19-laurent.pinchart@ideasonboard.com