dt-bindings: display: renesas,rzg2l-du: Refuse port@1 for RZ/G2UL

dt-bindings: display: renesas,rzg2l-du: Refuse port@1 for RZ/G2UL

The RZ/G2UL DU supports only a single port@0 DPI. Explicitly refuse
port@1 in the ports node.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/20260519160825.4082566-2-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>