arm64: dts: rockchip: rk356x: Add VOP2 nodes

The VOP2 is the display output controller on the RK3568. Add the node
for it to the dtsi file along with the required display-subsystem node
and the iommu node.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220422072841.2206452-17-s.hauer@pengutronix.de


Signed-off-by: Heiko Stuebner <heiko@sntech.de>