ARM: kprobes: Reject probing of STREX and LDREX instructions

The emulation code for STREX and LDREX instructions is faulty, however,
rather than attempting to fix this we reject probes of these
instructions. We do this because they can never succeed in gaining
exclusive access as the exception framework clears the exclusivity
monitor when a probes breakpoint is hit. (This is a general problem
when probing all instructions executing between a LDREX and its
corresponding STREX and can lead to infinite retry loops.)

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