The KUnit documentation [1] suggests allowing build tests as a module.

In addition, it is recommended [2] to use snake case names for
kunit_suite and test cases.

Change the Kconfig entry from bool to tristate and stick to the naming
conventions to avoid style issues with future tests.

Link: https://docs.kernel.org/dev-tools/kunit/style.html#test-kconfig-entries  [1]
Link: https://www.kernel.org/doc/html/latest/dev-tools/kunit/style.html  [2]
Acked-by: Daniel Latypov <dlatypov@google.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>