net: atlantic: add defines for 10M and EEE 100M link mode

This patch adds defines for 10M and EEE 100M link modes, which are
supported by A2.

10M support is added in this patch series.
EEE is out of scope, but will be added in a follow-up series.

Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>