tests: mem_protect/mem_map: limit CPUs to 1 if incoherent cache

For CPUs with incoherent cache under SMP, the tests to read/write
buffer (... majority of tests here) may not work correctly if
the test thread jumps between CPUs. So use the test infrastructure
to limit the test to 1 CPU.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>