arm64: dts: rockchip: Add RGA2 support to rk356x

The rk3568 also features a RGA2 block. Add the necessary device tree
node.

Acked-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Link: https://lore.kernel.org/r/20230119-rk3568-rga-v1-2-43d4d14365e6@pengutronix.de


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