drm/omap: simplify DSI manual update code

Move dsi_ops into the main structure, since all other ops
are gone. Instead of checking the device type we can simply
check if dsi_ops are set.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-48-tomi.valkeinen@ti.com