Add mpu driver and remove interface library
from drivers

Add mpu driver for upstreaming

After removing of interface library,targets and applications
will list explicitly which libraries to link

Change-Id: Icfa449a2981093161f283e45b4d52ca6199371b8
diff --git a/drivers/mhu_dummy/src/mhu_dummy.cpp b/drivers/mhu_dummy/src/mhu_dummy.cpp
new file mode 100644
index 0000000..3ae51e7
--- /dev/null
+++ b/drivers/mhu_dummy/src/mhu_dummy.cpp
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2020-2021 Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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
+ *
+ * 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.
+ */
+
+#include <mhu_dummy.hpp>
+
+namespace Mailbox {
+
+MHUDummy::MHUDummy() {}
+MHUDummy::~MHUDummy() {}
+
+void MHUDummy::handleMessage() {
+    notify();
+}
+bool MHUDummy::sendMessage() {
+    return true;
+}
+
+} // namespace Mailbox