App: Add NS interface code moved from TF-M

Add NS interface code moved from TF-M. It includes OS wrapper headers
and RTX specific implementation of OS wrapper.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I0b88535eaa720b52d2090d5ed041987093df9d75
diff --git a/ns_interface/os_wrapper/mutex.h b/ns_interface/os_wrapper/mutex.h
new file mode 100644
index 0000000..e55ef70
--- /dev/null
+++ b/ns_interface/os_wrapper/mutex.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2017-2019, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+#ifndef __OS_WRAPPER_MUTEX_H__
+#define __OS_WRAPPER_MUTEX_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "common.h"
+
+/**
+ * \brief Creates a mutex for mutual exclusion of resources
+ *
+ * \return The handle of the created mutex on success or NULL on error
+ */
+void *os_wrapper_mutex_create(void);
+
+/**
+ * \brief Acquires a mutex that is created by \ref os_wrapper_mutex_create()
+ *
+ * \param[in] handle   The handle of the mutex to acquire. Should be one of the
+ *                     handles returned by \ref os_wrapper_mutex_create()
+ * \param[in] timeout  The maximum amount of time(in tick periods) for the
+ *                     thread to wait for the mutex to be available.
+ *                     If timeout is zero, the function will return immediately.
+ *                     Setting timeout to \ref OS_WRAPPER_WAIT_FOREVER will
+ *                     cause the thread to wait indefinitely
+ *
+ * \return \ref OS_WRAPPER_SUCCESS on success or \ref OS_WRAPPER_ERROR on error
+ */
+uint32_t os_wrapper_mutex_acquire(void *handle, uint32_t timeout);
+
+/**
+ * \brief Releases the mutex acquired previously
+ *
+
+ * \param[in] handle The handle of the mutex that has been acquired
+ *
+ * \return \ref OS_WRAPPER_SUCCESS on success or \ref OS_WRAPPER_ERROR on error
+ */
+uint32_t os_wrapper_mutex_release(void *handle);
+
+/**
+ * \brief Deletes a mutex that is created by \ref os_wrapper_mutex_create()
+ *
+ * \param[in] handle The handle of the mutex to be deleted
+ *
+ * \return \ref OS_WRAPPER_SUCCESS on success or \ref OS_WRAPPER_ERROR on error
+ */
+uint32_t os_wrapper_mutex_delete(void *handle);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __OS_WRAPPER_MUTEX_H__ */