PSA_ALG_HKDF_EXTRACT macro

Macro to build an HKDF-Extract algorithm. For example, `PSA_ALG_HKDF_EXTRACT(PSA_ALG_SHA_256)` is HKDF-Extract using HMAC-SHA-256. This key derivation algorithm uses the following inputs: - PSA_KEY_DERIVATION_INPUT_SALT is the salt. - PSA_KEY_DERIVATION_INPUT_SECRET is the input keying material used in the "extract" step. The inputs are mandatory and must be passed in the order above. Each input may only be passed once. \warning HKDF-Extract is not meant to be used on its own. PSA_ALG_HKDF should be used instead if possible. PSA_ALG_HKDF_EXTRACT is provided as a separate algorithm for the sake of protocols that use it as a building block. It may also be a slight performance optimization in applications that use HKDF with the same salt and key but many different info strings. \warning HKDF processes the salt as follows: first hash it with hash_alg if the salt is longer than the block size of the hash algorithm; then pad with null bytes up to the block size. As a result, it is possible for distinct salt inputs to result in the same outputs. To ensure unique outputs, it is recommended to use a fixed length for salt values.