certs: Break circular dependency when selftest is modular

JIRA: https://issues.redhat.com/browse/RHEL-81929



commit 04a93202ed7c3b451bf22d3ff4bcd379df27f299
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date:   Mon Oct 16 13:21:44 2023 +0800

    certs: Break circular dependency when selftest is modular

    The modular build fails because the self-test code depends on pkcs7
    which in turn depends on x509 which contains the self-test.

    Split the self-test out into its own module to break the cycle.

    Fixes: 3cde3174eb91 ("certs: Add FIPS selftests")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Herbert Xu <herbert.xu@redhat.com>