lib/prime_numbers: KUnit test should not select PRIME_NUMBERS

lib/prime_numbers: KUnit test should not select PRIME_NUMBERS

Enabling a (modular) test should not silently enable additional kernel
functionality, as that may increase the attack vector of a product.

Fix this by making PRIME_NUMBERS_KUNIT_TEST depend on PRIME_NUMBERS
instead of selecting it.

After this, one can safely enable CONFIG_KUNIT_ALL_TESTS=m to build
modules for all appropriate tests for ones system, without pulling in
extra unwanted functionality, while still allowing a tester to manually
enable PRIME_NUMBERS and this test suite on a system where PRIME_NUMBERS
is not enabled by default.  Resurrect CONFIG_PRIME_NUMBERS=m in
tools/testing/selftests/lib/config for the latter use case.

Fixes: 313b38a6ecb46db4 ("lib/prime_numbers: convert self-test to KUnit")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/40f8a40eef4930d3ac9febd205bc171eb04e171c.1744641237.git.geert@linux-m68k.org
Signed-off-by: Kees Cook <kees@kernel.org>