Cleaned up the Disassembler code a bit more. You can now request a disassembler

plugin by name on the command line for when there is more than one disassembler
plugin.

Taught the Opcode class to dump itself so that "disassembler -b" will dump
the bytes correctly for each opcode type. Modified all places that were passing
the opcode bytes buffer in so that the bytes could be displayed to just pass
in a bool that indicates if we should dump the opcode bytes since the opcode
now lives inside llvm_private::Instruction.

llvm-svn: 128290