selftests: vm: pkeys: use the correct page size on powerpc

Both 4K and 64K pages are supported on powerpc.  Parts of the selftest
code perform alignment computations based on the PAGE_SIZE macro which is
currently hardcoded to 64K for powerpc.  This causes some test failures on
kernels configured with 4K page size.

In some cases, we need to enforce function alignment on page size.  Since
this can only be done at build time, 64K is used as the alignment factor
as that also ensures 4K alignment.

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Cc: "Desnes A. Nunes do Rosario" <desnesn@linux.vnet.ibm.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Suchanek <msuchanek@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Link: http://lkml.kernel.org/r/5dcdfbf3353acdc90f315172e800b49f5ca21299.1585646528.git.sandipan@linux.ibm.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>