opcodes: blackfin: fix decoding of many invalid insns

opcodes: blackfin: fix decoding of many invalid insns

The Blackfin disassembler was originally based on the premise of parsing
valid opcodes all the time, so some of the opcode checking can be a bit
fuzzy.  This is exemplified in decoding of parallel insns where many
times things are decoded as invalid when in reality, they may not be
used in parallel combinations.  So add parallel checking to most insn
decoding routines so we see ILLEGAL and not just whatever insn happens
to be close to a valid mnemonic, as well as some additional sub-opcode
checks.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>