phylink: add support for 2500baseX and 10GbaseKR

Add support for handling the faster 2.5G and 10G link modes when used
with SFP modules.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>