dt-bindings: display: renesas,rzg2l-du: Document RZ/V2L DU bindings

Document DU found in RZ/V2L SoC. The DU block is identical to RZ/G2L
SoC and therefore use RZ/G2L fallback to avoid any driver changes.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20240218164840.57662-3-biju.das.jz@bp.renesas.com


Signed-off-by: Maxime Ripard <mripard@kernel.org>