tests: arm_mem_protect: Add a test for stack pointer manipulation

The Cortex-R architecture uses the threads stack to save context.
However, that is a security hole since a userspace thread could
manipulate the stack pointer before performing a system call and cause
the kernel to write to memory that it should not.  This test will sanity
check that the Cortex-R svc and isr routines do not write to a userspace
supplied stack.

Signed-off-by: Bradley Bolen <bbolen@lexmark.com>