kselftest: Move ksft helper module to common directory

Move the ksft python module, which provides generic helpers for
kselftests, to a common directory so it can be more easily shared
between different tests.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240705-dev-err-log-selftest-v2-2-163b9cd7b3c1@collabora.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>