crypto: hash - Add import/export interface

It is often useful to save the partial state of a hash function
so that it can be used as a base for two or more computations.

The most prominent example is HMAC where all hashes start from
a base determined by the key.  Having an import/export interface
means that we only have to compute that base once rather than
for each message.

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

include/crypto/internal/hash.h

@@ -66,11 +66,6 @@ static inline struct ahash_request *ahash_dequeue_request(
 	return ahash_request_cast(crypto_dequeue_request(queue));
 }
 
-static inline void *ahash_request_ctx(struct ahash_request *req)
-{
-	return req->__ctx;
-}
-
 static inline int ahash_tfm_in_queue(struct crypto_queue *queue,
 					  struct crypto_ahash *tfm)
 {