dt-bindings: update grf-binding for rv1108 SoCs

This patch adds the compatible of GRF and USBGRF for RV1108 SoCs.
Signed-off-by: Frank Wang <frank.wang@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

@@ -21,6 +21,7 @@ Required Properties:
    - "rockchip,rk3328-grf", "syscon": for rk3328
    - "rockchip,rk3368-grf", "syscon": for rk3368
    - "rockchip,rk3399-grf", "syscon": for rk3399
+   - "rockchip,rv1108-grf", "syscon": for rv1108
 - compatible: PMUGRF should be one of the following:
    - "rockchip,rk3368-pmugrf", "syscon": for rk3368
    - "rockchip,rk3399-pmugrf", "syscon": for rk3399
@@ -28,6 +29,8 @@ Required Properties:
    - "rockchip,rk3288-sgrf", "syscon": for rk3288
 - compatible: USB2PHYGRF should be one of the followings
    - "rockchip,rk3328-usb2phy-grf", "syscon": for rk3328
+- compatible: USBGRF should be one of the following
+   - "rockchip,rv1108-usbgrf", "syscon": for rv1108
 - reg: physical base address of the controller and length of memory mapped
   region.