net: phy: add support for new modes in phylib

Recently new modes have been added to ethtool.h, but the related
extension to phylib hasn't been done yet. So add support for these
modes.

v2:
- add missing 100Gbps and 50Gbps modes

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>