- defined constant ISA_HOLE_START (would be nice to include machine/pmap.h,   but it has too much baggage). - create a new routine 'unregister_device_interrupt', which is now used   instead of having two routines with the same code snippet. - Minor cleanups and commenting.
- defined constant ISA_HOLE_START (would be nice to include machine/pmap.h,
  but it has too much baggage).
- create a new routine 'unregister_device_interrupt', which is now used
  instead of having two routines with the same code snippet.
- Minor cleanups and commenting.

[ No functional changes, just moving things around ]

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase