net: phy: Add limkmode equivalents to some of the MII ethtool helpers

Add helpers which take a linkmode rather than a u32 ethtool for
advertising settings.

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