selftests/mm: give scripts execute permission

When run under run_vmtests.sh, test scripts were failing to run with
"permission denied" due to the scripts not being executable.

It is also annoying not to be able to directly invoke run_vmtests.sh,
which is solved by giving also it the execute permission.

Link: https://lkml.kernel.org/r/20230713135440.3651409-3-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: ryanhrob