drm/omap: dsi: convert to drm_panel

This converts the DSI module to expect common drm_panel display
drivers instead of dssdev based ones.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-33-tomi.valkeinen@ti.com