dt-bindings: arm: rockchip: Add PinePhone Pro bindings

Document board compatible names for Pine64 PinePhonePro.

https://wiki.pine64.org/wiki/PinePhone_ProSigned-off-by: Tom Fitzhenry <tom@tom-fitzhenry.me.uk>
Reviewed-by: Caleb Connolly <kc@postmarketos.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220815123004.252014-2-tom@tom-fitzhenry.me.ukSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -499,6 +499,11 @@ properties:
           - const: pine64,pinenote
           - const: rockchip,rk3566
 
+      - description: Pine64 PinePhonePro
+        items:
+          - const: pine64,pinephone-pro
+          - const: rockchip,rk3399
+
       - description: Pine64 Rock64
         items:
           - const: pine64,rock64