crypto: mxs-dcp - Optimize hashing

Optimize the hashing operation in the MXS-DCP by doing two adjustments:
1) Given that the output buffer for the hash is now always correctly aligned,
   we can just use the buffer for the DCP DMA to store the resulting hash.
   We thus get rid of one copying of data. Moreover, we remove an entry from
   dcp_coherent_block{} and thus lower the memory footprint of the driver.
2) We map the output buffer for the hash for DMA only in case we will output
   the hash, not always, as it was now.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>