drm/omap: hdmi4: Simplify EDID read

Now that the omap_dss_device EDID read operation has been removed,
simplify the bridge-based EDID access by merging multiple functions
together.

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/20200226112514.12455-44-laurent.pinchart@ideasonboard.com