dt-bindings: Add doc for FriendlyARM NanoPi R5C

Add devicetree binding documentation for the FriendlyARM NanoPi R5C.
Acked-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: NTianling Shen <cnsztl@gmail.com>
Link: https://lore.kernel.org/r/20230318083745.6181-3-cnsztl@gmail.comSigned-off-by: NHeiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -201,9 +201,11 @@ properties:
               - friendlyarm,nanopi-r4s-enterprise
           - const: rockchip,rk3399
 
-      - description: FriendlyElec NanoPi R5S board
+      - description: FriendlyElec NanoPi R5 series boards
         items:
-          - const: friendlyarm,nanopi-r5s
+          - enum:
+              - friendlyarm,nanopi-r5c
+              - friendlyarm,nanopi-r5s
           - const: rockchip,rk3568
 
       - description: GeekBuying GeekBox