net: sxgbe: remove sxgbe_config

sxgbe_config() denies changing the base address and interrupt, and
ignores all other 'struct ifmap' members, which means that it is useless
as is, so let's remove it.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>