net: atlantic: A2: report link partner capabilities

This patch adds link partner capabilities reporting support on A2.
In particular, the following capabilities are available for reporting:
* link rate;
* EEE;
* flow control.

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