dt-bindings: phy-rockchip-inno-usb2: add rockchip,usbgrf property

Add rockchip,usbgrf property to support the registers of usb-phy
that are distributed in grf and usbgrf on some special Rockchip
SoCs (e.g RV1108).
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/phy-rockchip-inno-usb2.txt

@@ -18,6 +18,10 @@ Optional properties:
 		 usb-phy output 480m and xin24m.
 		 Refer to clk/clock-bindings.txt for generic clock
 		 consumer properties.
+ - rockchip,usbgrf : phandle to the syscon managing the "usb general
+		 register files". When set driver will request its
+		 phandle as one companion-grf for some special SoCs
+		 (e.g RV1108).
 
 Required nodes : a sub-node is required for each port the phy provides.
 		 The sub-node name is used to identify host or otg port,