Heres a patch I've had for a while, it removes a bunch of debugger code
which is good :) The next patch will sanitise it (and the rest of the
debugger hooks).

Various xmon cleanups

- recover from bad SPR read/write (we get a program check)
- remove some old code (bat and segment register stuff)
- update the help text to match reality
- add a "press ? for help" when xmon first appears to make rusty happy
- protect against flushing bad parts of memory from Milton
- dont print iseries specific stuff on pseries in SPR dump (S)
- add code to dump the segment table or SLB
- remove a number of functions that wouldnt work on LPAR