dt-bindings: arm: rockchip: add Radxa ROCK 3C

The Radxa ROCK 3C is a similar board to the
Radxa ROCK 3A with the Rockchip RK3566 SoC.
Add devicetree binding documentation for it.
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20240428123618.72170-2-amadeus@jmu.edu.cnSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -799,6 +799,11 @@ properties:
           - const: radxa,rock3a
           - const: rockchip,rk3568
 
+      - description: Radxa ROCK 3C
+        items:
+          - const: radxa,rock-3c
+          - const: rockchip,rk3566
+
       - description: Radxa ROCK 5A
         items:
           - const: radxa,rock-5a