dt-bindings: add doc for Firefly ROC-RK3328-PC

Add devicetree binding documentation for the Firefly ROC-RK3328-PC.
Signed-off-by: NLevin Du <djw@t-chip.com.cn>
Acked-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210709080126.17045-2-djw@t-chip.com.cnSigned-off-by: NHeiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -115,6 +115,11 @@ properties:
           - const: firefly,roc-rk3328-cc
           - const: rockchip,rk3328
 
+      - description: Firefly ROC-RK3328-PC
+        items:
+          - const: firefly,roc-rk3328-pc
+          - const: rockchip,rk3328
+
       - description: Firefly ROC-RK3399-PC
         items:
           - enum: