dt-bindings: net: wiznet: add w5x00 support

Add bindings for Wiznet's w5x00 series of SPI interfaced Ethernet chips.

Based on the bindings for microchip,enc28j60.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/wiznet,w5x00.txt

+* 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 */
+	};
+};