Add Sun-3 VME support (by Sam Creasey):
  - Added VME version of the Sun-3 NCR5380 scsi driver.
  - Modified the Sun-3 dvma routines to support VME.
  - Added sun3_map_test() -- uses the ex_table to trap faults on VME mappings
    in order to determine if a card is present.  This seems a little hackish to
    be, but:
      1) All changes are entirely within Sun3-only code paths,
      2) netbsd, sunos, and mach all use this mechanism for VME probes anyway.