tests: arch: arm mem protection check CPU scrubs regs after syscall

To improve Zephyr security, I decided to create a test
test_after_syscall_cpu_scrubs_regs
I think necessary to check upon exit of a system call back
to the calling thread, the kernel scrubs CPU registers for sensitive
data.

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>