mii: add support for Atheros AR803x 10/100/1000 PHY

[bz]

Summary

Add very basic support for the AR8035 (or probably AR803x) PHY(s)
needing to check a special status register for the actual link
information (speed, duplex).
There is a lot more the PHY can do (loop, cable test, ..) which
we do not yet implement (or not until we can test).

This PHY is found on SolidRun's HoneyComb.

[bz]

atphy will do just fine.