PSA_ALG_ED25519PH macro

Edwards-curve digital signature algorithm with prehashing (HashEdDSA), using SHA-512 and the Edwards25519 curve. See #PSA_ALG_PURE_EDDSA regarding context support and the signature format. This algorithm is Ed25519 as specified in RFC 8032. The curve is Edwards25519. The prehash is SHA-512. The hash function used internally is SHA-512. This is a hash-and-sign algorithm: to calculate a signature, you can either: - call psa_sign_message() on the message; - or calculate the SHA-512 hash of the message with psa_hash_compute() or with a multi-part hash operation started with psa_hash_setup(), using the hash algorithm #PSA_ALG_SHA_512, then sign the calculated hash with psa_sign_hash(). Verifying a signature is similar, using psa_verify_message() or psa_verify_hash() instead of the signature function.