selftests: mm: skip whole test instead of failure

selftests: mm: skip whole test instead of failure

Some architectures don't support userfaultfd.  Skip running the whole test
on them instead of registering the failure.

Link: https://lkml.kernel.org/r/20231103182343.2874015-1-usama.anjum@collabora.com
Fixes: 46fd75d4a3c9 ("selftests: mm: add pagemap ioctl tests")
Reported-by: Ryan Roberts <ryan.roberts@arm.com>
Closes: https://lore.kernel.org/all/f8463381-2697-49e9-9460-9dc73452830d@arm.com
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>