This patch makes use of arm64 AES instructions to accelerate AES computation
and only supports optimization on Linux for arm64

name        old time/op    new time/op     delta
Encrypt-32     255ns ± 0%       26ns ± 0%   -89.73%
Decrypt-32     256ns ± 0%       26ns ± 0%   -89.77%
Expand-32      990ns ± 5%      901ns ± 0%    -9.05%

name        old speed      new speed       delta
Encrypt-32  62.5MB/s ± 0%  610.4MB/s ± 0%  +876.39%
Decrypt-32  62.3MB/s ± 0%  610.2MB/s ± 0%  +879.6%

Fixes #18498

Change-Id: If416e5a151785325527b32ff72f6da3812493ed0
Reviewed-on: https://go-review.googlesource.com/64490
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>