net: add Xilinx emac lite device driver

This patch adds support for the Xilinx Ethernet Lite device.  The
soft logic core from Xilinx is typically used on Virtex and Spartan
designs attached to either a PowerPC or a Microblaze processor.

Signed-off-by: Sadanand M <sadanan@xilinx.com>
Signed-off-by: John Linn <john.linn@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>