selftests/mm: check that PAGEMAP_SCAN returns correct categories

Right now, tests read page flags from /proc/pid/pagemap files.  With this
change, tests will check that PAGEMAP_SCAN return correct information too.

[colin.i.king@gmail.com: fix spelling mistake "succedded" -> "succeeded"]
  Link: https://lkml.kernel.org/r/20231121093104.1728332-1-colin.i.king@gmail.com
Link: https://lkml.kernel.org/r/20231106220959.296568-2-avagin@google.com


Signed-off-by: Andrei Vagin <avagin@google.com>
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
[avagin@google.com: allow running tests on old kernels]
  Link: https://lkml.kernel.org/r/20231117181127.2574897-1-avagin@google.com


Signed-off-by: Andrew Morton <akpm@linux-foundation.org>