Documentation: bindings: net: add the Marvell PXA168 Ethernet controller

This adds the binding documentation for the Marvell PXA168 Ethernet
controller, following its DT support.
Signed-off-by: NAntoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell-pxa168.txt

+* Marvell PXA168 Ethernet Controller
+
+Required properties:
+- compatible: should be "marvell,pxa168-eth".
+- reg: address and length of the register set for the device.
+- interrupts: interrupt for the device.
+- clocks: pointer to the clock for the device.
+
+Optional properties:
+- port-id: Ethernet port number. Should be '0','1' or '2'.
+- #address-cells: must be 1 when using sub-nodes.
+- #size-cells: must be 0 when using sub-nodes.
+- phy-handle: see ethernet.txt file in the same directory.
+- local-mac-address: see ethernet.txt file in the same directory.
+
+Sub-nodes:
+Each PHY can be represented as a sub-node. This is not mandatory.
+
+Sub-nodes required properties:
+- reg: the MDIO address of the PHY.
+
+Example:
+
+	eth0: ethernet@f7b90000 {
+		compatible = "marvell,pxa168-eth";
+		reg = <0xf7b90000 0x10000>;
+		clocks = <&chip CLKID_GETH0>;
+		interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+		phy-handle = <&ethphy0>;
+
+		ethphy0: ethernet-phy@0 {
+			reg = <0>;
+		};
+	};