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.com


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