crypto: hash - move "ahash wrapping shash" functions to ahash.c

The functions that are involved in implementing the ahash API on top of
an shash algorithm belong better in ahash.c, not in shash.c where they
currently are.  Move them.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>