VtsKernelEncryptionTest: add a missing license header

.h files are supposed to have a license header too.

Change-Id: I4a4384975eaa21000242b9496a83e6041ca8a823
diff --git a/encryption/vts_kernel_encryption.h b/encryption/vts_kernel_encryption.h
index f335c84..92f8ef3 100644
--- a/encryption/vts_kernel_encryption.h
+++ b/encryption/vts_kernel_encryption.h
@@ -1,3 +1,18 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * 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.
+ */
 #pragma once
 
 #include <gtest/gtest.h>