Add MPS configuration header

This commit introduces the internal MPS header `mps/common.h`
which will subsequently be populated with MPS-specific compile-time
options and helper macros. For now, it's a stub.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>

library/mps/common.h

@@ -0,0 +1,31 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  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
+ *
+ *  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.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file common.h
+ *
+ * \brief Common functions and macros used by MPS
+ */
+
+#ifndef MBEDTLS_MPS_COMMON_H
+#define MBEDTLS_MPS_COMMON_H
+
+/* To be populated */
+
+#endif /* MBEDTLS_MPS_COMMON_H */