net: sfp: augment SFP parsing with phy_interface_t bitmap

We currently parse the SFP EEPROM to a bitmap of ethtool link modes,
and then attempt to convert the link modes to a PHY interface mode.
While this works at present, there are cases where this is sub-optimal.
For example, where a module can operate with several different PHY
interface modes.

To start addressing this, arrange for the SFP EEPROM parsing to also
provide a bitmap of the possible PHY interface modes.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>