Documentation: DT: net: Add Xilinx gmiitorgmii converter device tree binding documentation

XILINX GMIITORGMII Converter Driver Device Tree Bindings

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The Gigabit Media Independent Interface (GMII) to Reduced Gigabit Media

Independent Interface (RGMII) core provides the RGMII between RGMII-compliant

Ethernet physical media devices (PHY) and the Gigabit Ethernet controller.

This core can be used in all three modes of operation(10/100/1000 Mb/s).

The Management Data Input/Output (MDIO) interface is used to configure the

Speed of operation. This core can switch dynamically between the three

Different speed modes by configuring the conveter register through mdio write.

This converter sits between the ethernet MAC and the external phy.

MAC <==> GMII2RGMII <==> RGMII_PHY

For more details about mdio please refer phy.txt file in the same directory.

Required properties:

- compatible	: Should be "xlnx,gmii-to-rgmii-1.0"

- reg		: The ID number for the phy, usually a small integer

- phy-handle	: Should point to the external phy device.

		  See ethernet.txt file in the same directory.

Example:

	mdio {

		#address-cells = <1>;

		#size-cells = <0>;

		phy: ethernet-phy@0 {

			......

		};

		gmiitorgmii: gmiitorgmii@8 {

			compatible = "xlnx,gmii-to-rgmii-1.0";

			reg = <8>;

			phy-handle = <&phy>;

		};

	};