Adapt config.py to configuration file split

[ronald-cron-arm]

For the repo split, we plan to move all configuration options but the TLS and x509 ones from mbedtls_config.h to crypto_config.h that will become the TF-PSA-Crypto configuration file and probably be renamed tf_psa_crypto_config.h.

We need to adapt config.py. Same options, same interface but handles both mbedtls_config.h and tf_psa_crypto_config.h.

Depends on #9157.