net: Add MOXA ART SoCs ethernet driver

The MOXA UC-711X hardware(s) has an ethernet controller that seem
to be developed internally. The IC used is "RTL8201CP".

Since there is no public documentation, this driver is mostly the
one published by MOXA that has been heavily cleaned up / ported
from linux 2.6.9.

Signed-off-by: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>