crypto: Kconfig - allow tests to be disabled when manager is disabled

The library code uses CRYPTO_MANAGER_DISABLE_TESTS to conditionalize its
tests, but the library code can also exist without CRYPTO_MANAGER. That
means on minimal configs, the test code winds up being built with no way
to disable it.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>