dnet: Dave DNET ethernet controller driver (updated)

Driver for Dave DNET ethernet controller found on Dave/DENX QongEVB-LITE
FPGA. Heavily based on Dave sources, I've just adopted it to current
kernel version and done some code cleanup.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>