RFA: PowerPC: add segment register numbers

[Jim Blandy]

Kevin Buettner <kevinb@redhat.com> writes:
> A patch which does the latter would be welcome.  Consider it preapproved.

I was writing this patch and noticed some odd code in rs6000_gdbarch_init:

  /* Select instruction printer.  */
  if (arch == power)
    set_gdbarch_print_insn (gdbarch, print_insn_rs6000);
  else
    set_gdbarch_print_insn (gdbarch, gdb_print_insn_powerpc);

Now, 'arch' is an enum, and 'power' is a boolean.  So we've been using
gdb_print_insn_powerpc on rs6000 machines for some time --- the
incorrect code was introduced in r1.49, in Apr 2002.

So I'd like to actually try to test this patch on an RS6000 before
committing it.  :)