selftests/powerpc: Add subpage protection self test.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

mpe: Fix compile errors and formatting. Add tempfile logic to Makefile.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>