sxgbe: Add device-tree binding support document

* Samsung 10G Ethernet driver (SXGBE)

Required properties:

- compatible: Should be "samsung,sxgbe-v2.0a"

- reg: Address and length of the register set for the device

- interrupt-parent: Should be the phandle for the interrupt controller

  that services interrupts for this device

- interrupts: Should contain the SXGBE interrupts

  These interrupts are ordered by fixed and follows variable

  trasmit DMA interrupts, receive DMA interrupts and lpi interrupt.

  index 0 - this is fixed common interrupt of SXGBE and it is always

  available.

  index 1 to 25 - 8 variable trasmit interrupts, variable 16 receive interrupts

  and 1 optional lpi interrupt.

- phy-mode: String, operation mode of the PHY interface.

  Supported values are: "sgmii", "xgmii".

- samsung,pbl: Integer, Programmable Burst Length.

  Supported values are 1, 2, 4, 8, 16, or 32.

- samsung,burst-map: Integer, Program the possible bursts supported by sxgbe

  This is an interger and represents allowable DMA bursts when fixed burst.

  Allowable range is 0x01-0x3F. When this field is set fixed burst is enabled.

  When fixed length is needed for burst mode, it can be set within allowable

  range.

Optional properties:

- mac-address: 6 bytes, mac address

- max-frame-size: Maximum Transfer Unit (IEEE defined MTU), rather

		  than the maximum frame size.

Example:

	aliases {

		ethernet0 = <&sxgbe0>;

	};

	sxgbe0: ethernet@1a040000 {

		compatible = "samsung,sxgbe-v2.0a";

		reg = <0 0x1a040000 0 0x10000>;

		interrupt-parent = <&gic>;

		interrupts = <0 209 4>, <0 185 4>, <0 186 4>, <0 187 4>,

			     <0 188 4>, <0 189 4>, <0 190 4>, <0 191 4>,

			     <0 192 4>, <0 193 4>, <0 194 4>, <0 195 4>,

			     <0 196 4>, <0 197 4>, <0 198 4>, <0 199 4>,

			     <0 200 4>, <0 201 4>, <0 202 4>, <0 203 4>,

			     <0 204 4>, <0 205 4>, <0 206 4>, <0 207 4>,

			     <0 208 4>, <0 210 4>;

		samsung,pbl = <0x08>

		samsung,burst-map = <0x20>

		mac-address = [ 00 11 22 33 44 55 ]; /* Filled in by U-Boot */

		max-frame-size = <9000>;

		phy-mode = "xgmii";

	};