drm: mxsfb: Remove mxsfb_devdata unused fields

The debug0 and ipversion fields of the mxsfb_devdata structure are
unused. Remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200727020654.8231-16-laurent.pinchart@ideasonboard.com