drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver

This driver adds support for Xilinx 10/100/1000 AXI Ethernet.

It can be used, for instance, on Xilinx boards with a Microblaze
architecture like the ML605.

The patch is against the latest net-next tree and checkpatch clean.

Signed-off-by: Ariane Keller <ariane.keller@tik.ee.ethz.ch>
Signed-off-by: Daniel Borkmann <daniel.borkmann@tik.ee.ethz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>