all: rename crypto/internal/fips to crypto/internal/fips140

Sometimes we've used the 140 suffix (GOFIPS140, crypto/fips140)
and sometimes not (crypto/internal/fips, cmd/go/internal/fips).
Use it always, to avoid having to remember which is which.

Also, there are other FIPS standards, like AES (FIPS 197), SHA-2 (FIPS 180),
and so on, which have nothing to do with FIPS 140. Best to be clear.

For #70123.

Change-Id: I33b29dabd9e8b2703d2af25e428f88bc81c7c307
Reviewed-on: https://go-review.googlesource.com/c/go/+/630115
Reviewed-by: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>

prf.go

@@ -7,7 +7,7 @@ package tls
 import (
 	"crypto"
 	"crypto/hmac"
-	"crypto/internal/fips/tls12"
+	"crypto/internal/fips140/tls12"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"