Keep module compatibility with mbedtls 2.x (old LTS branch).
A patch has been added to allow compiling after removing all the `psa_*`
files from the library folder (will look into upstreaming it).
Note: mbedTLS 3.6 finally enabled TLSv1.3 by default, but it requires
some module changes, and to enable PSA crypto (new "standard" API
specification), so it might be best done in a separate commit/PR.
