net: atlantic: add fw configuration memory area

Device FW has a separate memory area where various
config fields are stored and could be used by the
driver.

Here we modify download/upload infrastructure to
allow accessing this area.

Lateron this will be used to configure various behaviours

Signed-off-by: Nikita Danilov <ndanilov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>