These are needed for some particular port configurations where the default
speed isn't suitable for all link speed types. (Ie, changing 10/100/1000MBit
PLL rate requires a similar MII clock rate, rather than a fixed MII rate.)
This is:
* only currently implemented for the ar71xx;
* isn't used anywhere (yet), as the final interface for this hasn't yet
been determined.
Each of these SoCs have different devices, different hardware initialisation
methods and, quite likely, different quirks. These functions will abstract
out the SoC differences and keep these differences out of the drivers (eg
USB init, if_arge, etc.)
