Add bfe(4) support from FreeBSD.

Add bfe(4) support from FreeBSD.
Initial code submitted by Peter Avalos <pavalos@theshell.com>.

Changes to the FreeBSD version:
- make the code consistent w.r.t. style(9)
- remove some unused entries from bfe_softc
- use the PCI IDs from pcidevs.h
- use BUS_DMA_WAITOK since the allocation is done in bfe_attach before
  the interrupt is registered and sleeping is therefore safe
- fix some warnings in the code about signed/unsigned comparisions