drm/omap: hdmi5: Register a drm_bridge for EDID read

In order to integrate with a chain of drm_bridge, the internal HDMI5
encoder has to expose the EDID read operation through the drm_bridge
API. Register a bridge at initialisation time to do so.

For the time being make the next bridge in the chain optional as the
HDMI output is still based on omap_dss_device. The create_connector
argument to the bridge attach function is also ignored for the same
reason. This will be changed later when removing the related
omapdrm-specific display drivers.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
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/20200226112514.12455-33-laurent.pinchart@ideasonboard.com