Interface: TF-M specific log API

Provide a TF-M specific log API. Put the source in 'interface' folder
since this file are referenced by multiple components, such as bl2,
non-secure application and secure firmware. The sources are included
into SPRTL building and as part of SPRTL.
The fundamental API is 'tfm_log_printf' which supports basic formats
like 'sdicpuxX' and '%' as the format leading and escape.

Change-Id: I6d0f89ab16c3e00f8e71129a06f89dc206733733
Signed-off-by: Mingyang Sun <mingyang.sun@arm.com>
diff --git a/interface/include/log/tfm_log_raw.h b/interface/include/log/tfm_log_raw.h
new file mode 100644
index 0000000..7a5a942
--- /dev/null
+++ b/interface/include/log/tfm_log_raw.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2019, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+#ifndef __TFM_LOG_RAW_H__
+#define __TFM_LOG_RAW_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \brief Prints log messages
+ *
+ * \param[in]   fmt     Formatted string
+ * \param[in]   ...     Viriable length argument
+ *
+ * \return              Number of chars printed
+ *
+ * \note                This function has the similar input argument format as
+ *                      the 'printf' function. But it supports only some basic
+ *                      formats like 'sdicpuxX' and '%'. It will output
+ *                      "[Unsupported Tag]" when none of the above formats match
+ *
+ * \details             The following output formats are supported.
+ *                      %s - string
+ *                      %d - decimal signed integer (same for %i)
+ *                      %u - decimal unsigned integer
+ *                      %x - hex in lowercase
+ *                      %X - hex in uppercase
+ *                      %p - hex address of a pointer in lowercase
+ *                      %c - character
+ *                      %% - the '%' symbol
+ */
+int tfm_log_printf(const char *fmt, ...);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __TFM_LOG_RAW_H__ */