drm/omap: panel-dsi-cm: convert to transfer API

This converts the panel-dsi-cm driver to use the transfer
API instead of specific functions, so that the specific
functions can be unexported and squashed into the generic
transfer function.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-7-tomi.valkeinen@ti.com