use crypto/sha256 only for FIPS 140-2 compliance (#14983)

It would seem like the PR #11623 had chewed more
than it wanted to, non-fips build shouldn't really
be forced to use slower crypto/sha256 even for
presumed "non-performance" codepaths. In MinIO
there are really no "non-performance" codepaths.
This assumption seems to have had an adverse
effect in certain areas of CPU usage.

This PR ensures that we stick to sha256-simd
on all non-FIPS builds, our most common build
to ensure we get the best out of the CPU at
any given point in time.

cmd/streaming-signature-v4.go

@@ -22,7 +22,6 @@ package cmd
 import (
 	"bufio"
 	"bytes"
-	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"hash"
@@ -32,6 +31,7 @@ import (
 
 	humanize "github.com/dustin/go-humanize"
 	"github.com/minio/minio/internal/auth"
+	"github.com/minio/minio/internal/hash/sha256"
 	xhttp "github.com/minio/minio/internal/http"
 )