When generating a split key or hashing the key, DMA mapping the key
buffers coming directly from user is incorrect, since they are
not guaranteed to be DMAable.

Update driver to first copy user-provided key in the output buffer
("key_out") and then use this buffer for in-place computation
(split key generation, respectively key hashing).
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>