dt-bindings: usb: new ehci-npcm7xx dt

Device Tree documentation for Nuvoton npcm7xx EHCI.
Signed-off-by: Avi Fishman <AviFishman70@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/npcm7xx-usb.txt

+Nuvoton NPCM7XX SoC USB controllers:
+-----------------------------
+
+EHCI:
+-----
+
+Required properties:
+- compatible: "nuvoton,npcm750-ehci"
+- interrupts: Should contain the EHCI interrupt
+- reg:        Physical address and length of the register set for the device
+
+Example:
+
+	ehci1: usb@f0806000 {
+		compatible = "nuvoton,npcm750-ehci";
+		reg = <0xf0806000 0x1000>;
+		interrupts = <0 61 4>;
+	};