ARM: kprobes-test: use <asm/opcodes.h> for Thumb instruction building

The kprobes test will build certain instructions incorrectly if building
big endian as .word/.short output gets endian-swapped by the linker.
Change to using <asm/opcodes.h> and __inst_thumbXX() to produce instructions.
Acked-by: NJon Medhurst <tixy@linaro.org>
Signed-off-by: NBen Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: NTaras Kondratiuk <taras.kondratiuk@linaro.org>