net: phylink: use supported_interfaces for phylink validation

If the network device supplies a supported interface bitmap, we can use
that during phylink's validation to simplify MAC drivers in two ways by
using the supported_interfaces bitmap to:

1. reject unsupported interfaces before calling into the MAC driver.
2. generate the set of all supported link modes across all supported
   interfaces (used mainly for SFP, but also some 10G PHYs.)

Suggested-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>