Change from using #if to #ifdef, since #if can't cope with string
constants.

Move ISA probe address logic from config.c into isa.c, create header file
config/isa.h.

Removed CONFIG_{PCI,ISA,PCMCIA}, since buses are now always compiled and
linked in only if required by the individual driver objects.

ROMs (AFAIK).

with generated headers.

Don't use -MP to generate phony rules for included files, otherwise
make won't use the pattern rule for config/%.h.  :(

timestamp on config.h to match the oldest fragment, to prevent make
from always attempting to rebuild the fragments.

header files.

Added REAL_FRAGMENT(), because it could conceivably be useful.

putchar() as well.

trick with "touch -B 2" doesn't work because the file that we're
carefully timestamping just gets deleted anyway.

list for any build, e.g.
  make bin/pnic.dsk DEBUG=pci,pnic
This will drag in debugging-enabled versions of pci.c and pnic.c.

since we probably shouldn't be doing this to arbitrary devices during a
PCI bus scan...

all return unsigned quantities.

quickly.

Prevented find_pci_device() from being an endless loop.