Correct mdio_oe naming, streamline to allow 1GHz capability

Created by: jrrk

The correction to the 1000BaseT mode is ready for review and merge. The one remaining issue is why we do not see interrupts. A very similar arrangement in LowRISC with Rocket does show the expected interrupts. I am seeing a slow down with all the new kernel options being enabled. This needs reviewing as well to see if they are all necessary.