* cipher/cipher-internal.h (gcry_cipher_handle): Add function pointers
for mode operations.
(_gcry_cipher_xts_crypt): Remove.
(_gcry_cipher_xts_encrypt, _gcry_cipher_xts_decrypt): New.
* cipher/cipher-xts.c (_gcry_cipher_xts_encrypt)
(_gcry_cipher_xts_decrypt): New.
* cipher/cipher.c (_gcry_cipher_setup_mode_ops): New.
(_gcry_cipher_open_internal): Setup mode routines.
(cipher_encrypt, cipher_decrypt): Remove.
(do_stream_encrypt, do_stream_decrypt, do_encrypt_none_unknown)
(do_decrypt_none_unknown): New.
(_gcry_cipher_encrypt, _gcry_cipher_decrypt, _gcry_cipher_setiv)
(_gcry_cipher_authenticate, _gcry_cipher_gettag)
(_gcry_cipher_checktag): Adapted to use mode routines through pointers.