AHC_FORCE_PIO - This forces the driver to use PIO even on systems that
say they have memory mapped the controller's registers. This
seems to fix Ken Lam's problems. I've also placed this option
in the GENERIC kernel file so that we are guaranteed to install
even on these flakey machines.
AHC_SHARE_SCBS - This option attempts to share the external SCB SRAM on
the 398X controllers allowing a totoll of 255 non-paged SCBs.
This doesn't work quite yet, so this option is mostly here to
help 398X owners to experiment and give me feedback until this
works properly.