ARM: Documentation: Update fec dts binding doc

This patch update fec devicetree binding doc that add Optional
    properties "fsl,num-tx-queues" and "fsl,num-rx-queues".

Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/fsl-fec.txt

@@ -16,6 +16,12 @@ Optional properties:
 - phy-handle : phandle to the PHY device connected to this device.
 - fixed-link : Assume a fixed link. See fixed-link.txt in the same directory.
   Use instead of phy-handle.
+- fsl,num-tx-queues : The property is valid for enet-avb IP, which supports
+  hw multi queues. Should specify the tx queue number, otherwise set tx queue
+  number to 1.
+- fsl,num-rx-queues : The property is valid for enet-avb IP, which supports
+  hw multi queues. Should specify the rx queue number, otherwise set rx queue
+  number to 1.
 
 Optional subnodes:
 - mdio : specifies the mdio bus in the FEC, used as a container for phy nodes