net: phylink: add ability to validate a set of interface modes

Rather than having the ability to validate all supported interface
modes or a single interface mode, introduce the ability to validate
a subset of supported modes.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
[ rebased on current net-next ]
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>