crypto: sha256-mb - Crypto computation (x8 AVX2)

This patch introduces the assembly routines to do SHA256 computation
on buffers belonging to several jobs at once.  The assembly routines
are optimized with AVX2 instructions that have 8 data lanes and using
AVX2 registers.

Signed-off-by: Megha Dey <megha.dey@linux.intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>