* src/gcrypt.h.in (GCRY_KDF_ONESTEP_KDF_MAC): New.
* cipher/kdf.c (onestep_kdf_mac_open, onestep_kdf_mac_compute): New.
(onestep_kdf_mac_final, onestep_kdf_mac_close): New.
(_gcry_kdf_open, _gcry_kdf_compute, _gcry_kdf_final, _gcry_kdf_close):
Add support for GCRY_KDF_ONESTEP_KDF_MAC.