net: phy: marvell10g: remove XGMII as an option for 88x3310

Remove XGMII as an option for the 88x3310 PHY driver, as the PHY doesn't
support XGMII's 32-bit data lanes.  It supports USXGMII, which is not
XGMII, but a single-lane serdes interface - see
https://developer.cisco.com/site/usgmii-usxgmii/



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>