selftest/vm: support xfail in mremap_test

Use ksft_test_result_xfail for the tests which are expected to fail.

Link: https://lkml.kernel.org/r/20220420215721.4868-3-sidhartha.kumar@oracle.com


Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>