ARM: kprobes: Decode 16-bit Thumb PUSH and POP instructions

These instructions are equivalent to

	stmdb sp!,{r0-r7,lr}
	ldmdb sp!,{r0-r7,pc}

and we emulate them by transforming them into the 32-bit Thumb
instructions

	stmdb r9!,{r0-r7,r8}
	ldmdb r9!,{r0-r7,r8}

This is simpler, and almost certainly executes faster, than writing
simulation functions.

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