net: phy: Add support for resolving 5G and 2.5G autoneg

Now that 2.5G and 5G can be represented in phydev->advertising and
phydev->lp_advertising, add these two links modes as possible
resolutions to auto negotiation.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>