This also adds a newbus interface that allows a SoC to override the
following settings:
- if_dwc specific SoC initialization;
- if_dwc descriptor type;
- if_dwc MII clock.
This seems to be an old version of the hardware descriptors but it is
still in use in a few SoCs (namely Allwinner A20 and Amlogic at least).
Tested on Cubieboard2 and Banana pi.
Tested for regressions on Altera Cyclone by br@ (old version).
Obtained from: NetBSD
5df539274f