hash: Enable hash_bytes128 optimization for aarch64.

hash: Enable hash_bytes128 optimization for aarch64.

"hash_bytes128" has two versions for 64 bits and 32 bits system. This
should be common optimization for their respective platforms. But 64 bits
version was only enabled in x86-64. This patch enable it for aarch64
platform.
Micro benchmarking test was run in two kinds of arm platform. It was
observed that 50% performance improvement in thunderX2 and 40% improvement
in TaiShan(Cortex-A72).

Signed-off-by: Yanqin Wei <Yanqin.Wei@arm.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>