dt-bindings: display: rockchip-dsi: add rk3568 compatible

The rk3568 uses the same dw-mipi-dsi controller as previous Rockchip
SOCs, so add a compatible string for it.
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220906174823.28561-2-macroalpha82@gmail.com

Documentation/devicetree/bindings/display/rockchip/dw_mipi_dsi_rockchip.txt

@@ -8,6 +8,7 @@ Required properties:
 	"rockchip,px30-mipi-dsi", "snps,dw-mipi-dsi"
 	"rockchip,rk3288-mipi-dsi", "snps,dw-mipi-dsi"
 	"rockchip,rk3399-mipi-dsi", "snps,dw-mipi-dsi"
+	"rockchip,rk3568-mipi-dsi", "snps,dw-mipi-dsi"
 - reg: Represent the physical address range of the controller.
 - interrupts: Represent the controller's interrupt to the CPU(s).
 - clocks, clock-names: Phandles to the controller's pll reference