Features
   * When a PSA driver for ECDH is present, it is now possible to disable
     MBEDTLS_ECDH_C in the build in order to save code size. For TLS 1.2
     key exchanges based on ECDH(E) to work, this requires
     MBEDTLS_USE_PSA_CRYPTO. Restartable/interruptible ECDHE operations in
     TLS 1.2 (ECDHE-ECDSA key exchange) are not supported in those builds yet,
     as PSA does not have an API for restartable ECDH yet.
