This change replaces all imports of "crypto/sha256" with
"github.com/minio/sha256-simd". The sha256-simd package
is faster on ARM64 (NEON instructions) and can take advantage
of AVX-512 in certain scenarios.
Fixes#5374
This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.
Updates are done safely by validating the downloaded
sha256 of the binary.
Fixes#4781