net: dsa: Add support for a switch reset gpio

Some boards have a gpio line tied to the switch reset pin. Allow this
gpio to be retrieved from the device tree, and take the switch out of
reset before performing the probe.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/dsa/dsa.txt

@@ -31,6 +31,8 @@ A switch child node has the following optional property:
 			  switch. Must be set if the switch can not detect
 			  the presence and/or size of a connected EEPROM,
 			  otherwise optional.
+- reset-gpios		: phandle and specifier to a gpio line connected to
+			  reset pin of the switch chip.
 
 A switch may have multiple "port" children nodes
 
@@ -114,6 +116,7 @@ Example:
 			#size-cells = <0>;
 			reg = <17 1>;	/* MDIO address 17, switch 1 in tree */
 			mii-bus = <&mii_bus1>;
+			reset-gpios = <&gpio5 1 GPIO_ACTIVE_LOW>;
 
 			switch1port0: port@0 {
 				reg = <0>;