dt-bindings: usb: DT bindings documentation for Broadcom IPROC USB Device controller.

The device node is used for UDCs integrated into Broadcom's
iProc family of SoCs'. The UDC is based on Synopsys Designware
Cores AHB Subsystem USB Device Controller IP.
Signed-off-by: Raviteja Garimella <raviteja.garimella@broadcom.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

Documentation/devicetree/bindings/usb/iproc-udc.txt

+Broadcom IPROC USB Device controller.
+
+The device node is used for UDCs integrated into Broadcom's
+iProc family (Northstar2, Cygnus) of SoCs'. The UDC is based
+on Synopsys Designware Cores AHB Subsystem Device Controller
+IP.
+
+Required properties:
+ - compatible: Add the compatibility strings for supported platforms.
+   For Broadcom NS2 platform, add "brcm,ns2-udc","brcm,iproc-udc".
+   For Broadcom Cygnus platform, add "brcm,cygnus-udc", "brcm,iproc-udc".
+ - reg: Offset and length of UDC register set
+ - interrupts: description of interrupt line
+ - phys: phandle to phy node.
+
+Example:
+	udc_dwc: usb@664e0000 {
+		compatible = "brcm,ns2-udc", "brcm,iproc-udc";
+		reg = <0x664e0000 0x2000>;
+		interrupts = <GIC_SPI 424 IRQ_TYPE_LEVEL_HIGH>;
+		phys = <&usbdrd_phy>;