dt-bindings: net: wiznet: add w5x00 support

* Wiznet w5x00

This is a standalone 10/100 MBit Ethernet controller with SPI interface.

For each device connected to a SPI bus, define a child node within

the SPI master node.

Required properties:

- compatible: Should be one of the following strings:

	      "wiznet,w5100"

	      "wiznet,w5200"

	      "wiznet,w5500"

- reg: Specify the SPI chip select the chip is wired to.

- interrupts: Specify the interrupt index within the interrupt controller (referred

              to above in interrupt-parent) and interrupt type. w5x00 natively

              generates falling edge interrupts, however, additional board logic

              might invert the signal.

- pinctrl-names: List of assigned state names, see pinctrl binding documentation.

- pinctrl-0: List of phandles to configure the GPIO pin used as interrupt line,

             see also generic and your platform specific pinctrl binding

             documentation.

Optional properties:

- spi-max-frequency: Maximum frequency of the SPI bus when accessing the w5500.

  According to the w5500 datasheet, the chip allows a maximum of 80 MHz, however,

  board designs may need to limit this value.

- local-mac-address: See ethernet.txt in the same directory.

Example (for Raspberry Pi with pin control stuff for GPIO irq):

&spi {

	ethernet@0: w5500@0 {

		compatible = "wiznet,w5500";

		reg = <0>;

		pinctrl-names = "default";

		pinctrl-0 = <&eth1_pins>;

		interrupt-parent = <&gpio>;

		interrupts = <25 IRQ_TYPE_EDGE_FALLING>;

		spi-max-frequency = <30000000>;

	};

};

&gpio {

	eth1_pins: eth1_pins {

		brcm,pins = <25>;

		brcm,function = <0>; /* in */

		brcm,pull = <0>; /* none */

	};

};