net: Add support for the OpenCores 10/100 Mbps Ethernet MAC.

This patch adds a platform device driver that supports the OpenCores 10/100
Mbps Ethernet MAC.

The driver expects three resources: one IORESOURCE_MEM resource defines the
memory region for the core's memory-mapped registers while a second
IORESOURCE_MEM resource defines the network packet buffer space. The third
resource, of type IORESOURCE_IRQ, associates an interrupt with the driver.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>