Massive overhaul of exca to help with the isa efforts:

Massive overhaul of exca to help with the isa efforts:
o chip_name arrays ifdef'd out.
o use the OLDCARD-like get/put functions so we can support differnt types
  of mappings.
o Write the beggings of is this a valid exca device and introduce more
  chipset support.

# this is partially a wip, but also needed because some other cahnges I've
# made require some of these changes.