Merge branch 'net-phy-add-interface-mode-PHY_INTERFACE_MODE_USXGMII'

Heiner Kallweit says:

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net: phy: add interface mode PHY_INTERFACE_MODE_USXGMII

Add support for interface mode USXGMII.

On Freescale boards LS1043A and LS1046A a warning may pop up now
because mode xgmii should be changed to usxgmii (as the used
Aquantia PHY doesn't support XGMII).
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Signed-off-by: David S. Miller <davem@davemloft.net>