drm/omap: Add infrastructure to support drm_bridge local to DSS outputs

drm/omap: Add infrastructure to support drm_bridge local to DSS outputs

In order to support drm_bridge-based pipeline, the internal HDMI
encoders will need to expose the EDID read operation through the
drm_bridge API, and thus to expose a drm_bridge instance corresponding
to the encoder. The HDMI encoders are however handled as omap_dss_device
instances, which conflicts with this requirement.

In order to move forward with the drm_bridge transition, add support for
creating drm_bridge instances local to DSS outputs. If a local bridge is
passed to the omapdss_device_init_output() function, it is used as the
first bridge in the chain, and the omap_dss_device.next_bridge field is
set to the next bridge for the use of the internal encoders' bridges.

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/20200226112514.12455-27-laurent.pinchart@ideasonboard.com