crypto: sha256 - Optimized sha256 x86_64 assembly routine with AVX instructions.

Provides SHA256 x86_64 assembly routine optimized with SSE and AVX instructions.
Speedup of 60% or more has been measured over the generic implementation.
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>