ARM: kprobes: Reject probing of undefined multiply instructions

The instructions space for 'Multiply and multiply-accumulate'
instructions contains some undefined patterns. We need to reject
probing of these because they may in future become defined and the
kprobes code may then emulate them faultily.

This has already happened with the new MLS instruction which this patch
also adds correct decoding for as well as tightening up other decoding
tests. (Before this patch the wrong emulation routine was being called
for MLS though it still produced correct results.)

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>