drm/omap: dsi: set trans_mode according to client mode_flags

The DSI host driver currently ignores the video mode flags in
client->mode_flags. Add the code to take the transfer mode from client's
mode_flags.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215104657.802264-60-tomi.valkeinen@ti.com