net: aquantia: implement EEE support

Support of Energy-Efficient Ethernet to aQuantia NIC's via ethtool
(according to the IEEE 802.3az specifications)

Signed-off-by: Yana Esina <yana.esina@aquantia.com>
Signed-off-by: Nikita Danilov <nikita.danilov@aquantia.com>
Tested-by: Nikita Danilov <nikita.danilov@aquantia.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>