net: atlantic: implement media detect feature via phy tunables

Mediadetect is another name for the EDPD (energy detect power down).
This feature allows device to save extra power when no link is available.

PHY goes into the extreme power saving mode and only periodically wakes up
and checks for the link.

AQC devices has fixed check period of 6 seconds

The feature may increase linkup time.

Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>