dt-bindings: add binding for rk3328-grf

This adds the compatible for the General Register Files on the new rk3328.
Signed-off-by: Liang Chen <cl@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/soc/rockchip/grf.txt

@@ -16,6 +16,7 @@ Required Properties:
    - "rockchip,rk3188-grf", "syscon": for rk3188
    - "rockchip,rk3228-grf", "syscon": for rk3228
    - "rockchip,rk3288-grf", "syscon": for rk3288
+   - "rockchip,rk3328-grf", "syscon": for rk3328
    - "rockchip,rk3368-grf", "syscon": for rk3368
    - "rockchip,rk3399-grf", "syscon": for rk3399
 - compatible: PMUGRF should be one of the following: