zephyr: arm_cleanup.c: use <.../cortex_m/cmsis.h>

Use <arch/arm/aarch32/cortex_m/cmsis.h> include instead of <zephyr.h> to
get access to Cortex-M CMSIS API. zephyr.h provides kernel API, does not
guarantee access to CPU internals.

Fixes: #699 "Building MCUBoot for Zephyr fails on multiple ARM boards"

Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>