This patch overhauls and fixes code related to crypto4xx_build_pd()

 * crypto4xx_build_pd() did not handle chained source scatterlist.
   This is fixed by replacing the buggy indexed-access of &src[idx]
   with sg_next() in the gather array setup loop.

 * The redundant is_hash, direction, save_iv and pd_ctl members
   in the crypto4xx_ctx struct have been removed.
    - is_hash can be derived from the crypto_async_request parameter.
    - direction is already part of the security association's
      bf.dir bitfield.
    - save_iv is unused.
    - pd_ctl always had the host_ready bit enabled anyway.
      (the hash_final case is rather pointless, since the ahash
       code has been deactivated).

 * make crypto4xx_build_pd()'s caller responsible for converting
   the IV to the LE32 format.

 * change crypto4xx_ahash_update() and crypto4xx_ahash_digest() to
   initialize a temporary destination scatterlist. This allows the
   removal of an ugly cast of req->result (which is a pointer to an
   u8-array) to a scatterlist pointer.

 * change crypto4xx_build_pd() return type to int. After all
   it returns -EINPROGRESS/-EBUSY.

 * fix crypto4xx_build_pd() thread-unsafe sa handling.
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>