Documentation: devicetree: add PHY lane swap binding

Add the documentation for PHY lane swapping.  This is a boolean entry to
notify the phy device drivers that the TX/RX lanes need to be swapped.
Signed-off-by: NJon Mason <jon.mason@broadcom.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/phy.txt

@@ -35,6 +35,10 @@ Optional Properties:
 - broken-turn-around: If set, indicates the PHY device does not correctly
   release the turn around line low at the end of a MDIO transaction.
 
+- enet-phy-lane-swap: If set, indicates the PHY will swap the TX/RX lanes to
+  compensate for the board being designed with the lanes swapped.
+
+
 Example:
 
 ethernet-phy@0 {