cross-reference the DH and RSA SECLEVEL to level of security mappings

cross-reference the DH and RSA SECLEVEL to level of security mappings

Since the DH check is used only in DHE-PSK ciphersuites, it's
easy to miss it when updating the RSA mapping. Add cross-references
so that they remain consistent.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15853)