net: ethernet: Use phy_set_max_speed() to limit advertised speed

Many Ethernet MAC drivers want to limit the PHY to only advertise a
maximum speed of 100Mbs or 1Gbps. Rather than using a mask, make use
of the helper function phy_set_max_speed().

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