SYS panels are not used, and have no defined DT bindings.  Remove their
support to avoid impeding DT support.  It can always be added back
later.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/4ccca2a5ac05c73ea9fd6e44b8bc443fd9d14e0d.1694767209.git.geert+renesas@glider.be