* cipher/rijndael-internal.h (rijndael_prepare_decfn_t): New.
(RIJNDAEL_context_s): New member 'prepare_decryption'.
* cipher/rijndael-padlock.c (_gcry_aes_padlock_prepare_decryption): New.
* cipher/rijndael.c (_gcry_aes_padlock_prepare_decryption): New.
(do_setkey): Setup 'ctx->prepare_decryption' for each acceleration type.
(prepare_decryption): Remove calls to other prepare decryption functions.
(check_decryption_preparation): Call 'ctx->prepare_decryption' instead
of 'prepare_decryption'.