ARM: kprobes: Reject probing of undefined media instructions

The instructions space for media 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.

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