Bring in the most recent copy of NetBSD's db_disasm, to fix bugs and add more
instructions.
* Fix several bugs in the disassembler, most notably the disassembly of the
rlwi* instructions, the original reason for bringing in this change.
* Add more registers to the SPR list
* Add more instructions to the opcode table
Obtained from: NetBSD
MFC after: 2 weeks