Opcode suffixes do not take into account prefix bytes

[nathanhjay]

I think we're not changing the suffix of sbb when it is prefixed.

On sbb, we use the 'l' prefix with %rax. The l-prefix should only be used for 64 bits in the case of floating point instructions, according to the rules imposed by gas.
Bytes: 4a 83 d8 f4
Dyninst Output: sbbl $0xfffffffffffffff4,%rax

We also use the 'l' prefix with %bp for sbb, which isn't correct.
Bytes: 66 83 dd c0
Dyninst Output: sbbl $0xc0,%bp