kirkwood: 6.1: backport Marvell 88E6171 init fix patch

kirkwood: 6.1: backport Marvell 88E6171 init fix patch

After commit de5c9bf40c45 ("net: phylink: require supported_interfaces to
be filled") Marvell 88e6171 switches fail to be probed:

[    1.263852] mv88e6085 f1072004.mdio-bus-mii:10: switch 0x1710 detected: Marvell 88E6171, revision 2
[    2.177654] mv88e6085 f1072004.mdio-bus-mii:10: OF node /ocp@f1000000/mdio-bus@72004/switch@10/ports/port@5 of CPU port 5 lacks the required "phy-mode" property
[    2.194230] mv88e6085 f1072004.mdio-bus-mii:10: phylink: error: empty supported_interfaces
[    2.202554] error creating PHYLINK: -22
[    2.214109] mv88e6085: probe of f1072004.mdio-bus-mii:10 failed with error -22

Upstream handled it. Lets backport patch.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>