MIPS: Alchemy: Add au1000-eth platform device

This patch makes the board code register the au1000-eth platform device. The
au1000-eth platform data can be overriden with the au1xxx_override_eth_cfg
function like it has to be done for the Bosporus board which uses a
different MAC/PHY setup.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Cc: David Miller <davem@davemloft.net>
Cc: linux-mips@linux-mips.org
Cc: netdev@vger.kernel.org
Patchwork: http://patchwork.linux-mips.org/patch/618/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>