Skip MPU fault tests for ARMv8-M

For enhanced security ARMv8-M firmware doesn't allow the hardfault
handler to be hooked by non-secure code. Because of this there is no
way to recover from the MPU fault tests. This PR disables those tests
until hardfault recovery is supported by secure firmware.

Author: c1728p9

TESTS/mbed_hal/mpu/main.cpp

@@ -178,10 +178,13 @@ utest::v1::status_t fault_override_teardown(const Case *const source, const size
 Case cases[] = {
     Case("MPU - init", fault_override_setup, mpu_init_test, fault_override_teardown),
     Case("MPU - free", fault_override_setup, mpu_free_test, fault_override_teardown),
+#if !((__ARM_ARCH_8M_BASE__ == 1U) || (__ARM_ARCH_8M_MAIN__ == 1U))
+    // Skip fault tests for ARMv8-M until a fault handler hook is provided
     Case("MPU - data fault", fault_override_setup, mpu_fault_test_data, fault_override_teardown),
     Case("MPU - bss fault", fault_override_setup, mpu_fault_test_bss, fault_override_teardown),
     Case("MPU - stack fault", fault_override_setup, mpu_fault_test_stack, fault_override_teardown),
     Case("MPU - heap fault", fault_override_setup, mpu_fault_test_heap, fault_override_teardown)
+#endif
 };
 
 utest::v1::status_t greentea_test_setup(const size_t number_of_cases)