net: phy: move phy_lookup_setting() and guts of phy_supported_speeds() to phy-core

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: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>