net: dm9000: Pass private data around for IO

Pass private data into IO accessors and use the base addresses of
IO and DATA window from the private data instead of using the hard
coded macros DM9000_IO/DM9000_DATA. Currently both the DM9000_IO
and DM9000_DATA are assigned to the respecive private data fields
for the non-DM case backward compatibility.

Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Ramon Fried <rfried.dev@gmail.com>