dt-bindings: arm: rockchip: add FriendlyARM NanoPi R2C Plus

Add devicetree binding documentation for the NanoPi R2C Plus.
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Tianling Shen <cnsztl@gmail.com>
Link: https://lore.kernel.org/r/20230513135307.26554-1-cnsztl@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -194,6 +194,7 @@ properties:
         items:
           - enum:
               - friendlyarm,nanopi-r2c
+              - friendlyarm,nanopi-r2c-plus
               - friendlyarm,nanopi-r2s
           - const: rockchip,rk3328