net: DM9000: Add support for byte EEPROM access

Given many versions of ethtool's reluctance to do anything other than
byte accesses to the EEPROM interface, it is easier to update the driver
to support byte accesses so that all the ethtool versions that have been
observed in Debian can write the EEPROM.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>