tests: arm: interrupt: test-case for stacking error check

We add a test case to verify that the Cortex-M fault
handling is able to catch stacking errors explicitly
due to exception entry frame stacking (that is, when
the Cortex-M MCU does not report Data Access Violation
MemManage fault with a valid MMFAR value, but only a
Stacking MemManage fault). We update the README file
accordingly.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>