net: phy: lxt: Export link partner advertising

Provide link partner advertising information.
Removed testing for gigabit modes, which is useless for a fast ethernet phy.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>