drm/omap: dpi: Register a drm_bridge

drm/omap: dpi: Register a drm_bridge

In order to integrate with a chain of drm_bridge, the internal DPI
output has to expose its operations through the drm_bridge API.
Register a bridge at initialisation time to do so and remove the
omap_dss_device operations that are now unused.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226112514.12455-49-laurent.pinchart@ideasonboard.com