selftests/mm: skip uffd hugetlb tests with insufficient hugepages

Now that run_vmtests.sh does not guarantee that the correct hugepage count
is available, add a check inside the userfaultfd hugetlb test to verify
the nr_hugepages count before continuing.

Link: https://lkml.kernel.org/r/20240306223714.320681-3-npache@redhat.com


Signed-off-by: Nico Pache <npache@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>