net: fec: parser max queue number from dt file

By default, the tx/rx queue number is 1, user can config the queue number
at DTS file like this:
	fsl,num-tx-queues=<3>;
	fsl,num-rx-queues=<3>

Since i.MX6SX enet-AVB IP support multi queues, so use multi queues
interface to allocate and set up an Ethernet device.

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>