ARM: kprobes: Add load_write_pc()

This writes a value to PC which was obtained as the result of a
LDR or LDM instruction. For ARMv5T and later this must perform
interworking.

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