Split the bits that have some duplication with disas_insn_new, from
those that should be the main topic of the conversion. This is the
first step towards removing duplicate decoding of prefixes between
disas_insn and disas_insn_new.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>