[CRYPTO] skcipher: Create default givcipher instances

This patch makes crypto_alloc_ablkcipher/crypto_grab_skcipher always
return algorithms that are capable of generating their own IVs through
givencrypt and givdecrypt.  Each algorithm may specify its default IV
generator through the geniv field.

For algorithms that do not set the geniv field, the blkcipher layer will
pick a default.  Currently it's chainiv for synchronous algorithms and
eseqiv for asynchronous algorithms.  Note that if these wrappers do not
work on an algorithm then that algorithm must specify its own geniv or
it can't be used at all.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/internal/skcipher.h

@@ -53,6 +53,8 @@ static inline struct crypto_ablkcipher *crypto_spawn_skcipher(
 				 crypto_skcipher_mask(0)));
 }
 
+int skcipher_null_givencrypt(struct skcipher_givcrypt_request *req);
+int skcipher_null_givdecrypt(struct skcipher_givcrypt_request *req);
 const char *crypto_default_geniv(const struct crypto_alg *alg);
 
 struct crypto_instance *skcipher_geniv_alloc(struct crypto_template *tmpl,