Currently, the kfence test suite could not run via "normal" means since
KUnit didn't support per-suite setup/teardown. So it manually called
internal kunit functions to run itself.
This has some downsides, like missing TAP headers => can't use kunit.py
to run or even parse the test results (w/o tweaks).

Use the newly added support and convert it over, adding a .kunitconfig
so it's even easier to run from kunit.py.

People can now run the test via
$ ./tools/testing/kunit/kunit.py run --kunitconfig=mm/kfence --arch=x86_64
...
[11:02:32] Testing complete. Passed: 23, Failed: 0, Crashed: 0, Skipped: 2, Errors: 0
[11:02:32] Elapsed time: 43.562s total, 0.003s configuring, 9.268s building, 34.281s running

Cc: kasan-dev@googlegroups.com
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>