net: phy: aquantia: add support for auto-negotiation configuration

Make use of the generic c45 code, plus code specific to the Aquantia
phy for 1000BaseT negotiation.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>