fdre: fix build error w/ assembler

Seems like different version of flex/bison in F18 somehow triggers
compile error.  This fixes it.
disasm: further work on a3xx disassembler..

Decoding a lot more opc's.. but I think the different instruction
categories have different # of bits for opc field, so for some of the
instruction categories this needs some more work..
disasm: restructure disassembler for instr categories

Restructure things to deal better with the multiple different
instruction encodings on a3xx.