fips: always enable AES in FIPS mode when using madmin (#11732)

This commit adds FIPS-specifc build tags to the madmin
package. When madmin is compiled with `--tags "fips"`
it will always use AES-GCM for encryption - not just
when an optimized AES implementation is available.

pkg/madmin/encrypt_fips.go

@@ -0,0 +1,22 @@
+// MinIO Cloud Storage, (C) 2021 MinIO, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build fips
+
+package madmin
+
+// useAES always returns true since AES is the only
+// option out of AES-GCM and ChaCha20-Poly1305 that
+// is approved by the NIST.
+func useAES() bool { return true }