Extending sys/dev/mii

[Juli Mallett]

> > The PHYs don't sit on arge1.  They sit on another device that the
> > driver bogusly assumes is tightly coupled to arge1, when in fact it
> > isn't.
>
> At least for AR7240/AR7242, MDIO control registers lie in the middle of
> register space used by if_arge.

That's a fine electrical and address-oriented understanding, but that
doesn't mean that a different functional conceptualization wouldn't lend
itself better to implementation. Fidelity to the memory layout is a neat
idea but not necessarily desirable or even reasonable.