dt-bindings: display: rockchip-vop: Document rv1126 vop

The VOP on Rockchip's RV1126 SoC is different from other SoC's
VOP implementations, so add a separate compatible for it.

Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230731110012.2913742-6-jagan@edgeble.ai