phy_lookup_setting() provides useful functionality in ethtool code
outside phylib.  Move it to phy-core and allow it to be re-used (eg,
in phylink) rather than duplicated elsewhere.  Note that this supports
the larger linkmode space.

As we move the phy settings table, we also need to move the guts of
phy_supported_speeds() as well.
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>