Import mbedtls-2.16.0

Imports mbedTLS 2.16.0 from https://github.com/ARMmbed/mbedtls.git
commit fb1972db23da ("Merge pull request #544 from ARMmbed/version-2.16")
(tag mbedtls-2.16.0).

Certain files will never be needed and are thus removed (reducing number
of lines to almost 50%):
rm -f circle.yml CMakeLists.txt DartConfiguration.tcl Makefile
rm -f .gitignore .travis.yml .pylint
rm -f include/.gitignore include/CMakeLists.txt library/.gitignore
rm -f library/CMakeLists.txt library/Makefile
rm -rf .git .github doxygen configs programs scripts tests visualc yotta

This is a complete overwrite of previous code so earlier changes in the
branch import/mbedtls-2.6.1 will be added on top of this commit to bring
the changes forward.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/havege.c b/lib/libmbedtls/mbedtls/library/havege.c
index aff307e..4dcac02 100644
--- a/lib/libmbedtls/mbedtls/library/havege.c
+++ b/lib/libmbedtls/mbedtls/library/havege.c
@@ -1,8 +1,8 @@
-// SPDX-License-Identifier: Apache-2.0
 /**
  *  \brief HAVEGE: HArdware Volatile Entropy Gathering and Expansion
  *
  *  Copyright (C) 2006-2015, 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.
@@ -36,14 +36,10 @@
 
 #include "mbedtls/havege.h"
 #include "mbedtls/timing.h"
+#include "mbedtls/platform_util.h"
 
 #include <string.h>
 
-/* Implementation that should never be optimized out by the compiler */
-static void mbedtls_zeroize( void *v, size_t n ) {
-    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
-}
-
 /* ------------------------------------------------------------------------
  * On average, one iteration accesses two 8-word blocks in the havege WALK
  * table, and generates 16 words in the RES array.
@@ -208,7 +204,7 @@
     if( hs == NULL )
         return;
 
-    mbedtls_zeroize( hs, sizeof( mbedtls_havege_state ) );
+    mbedtls_platform_zeroize( hs, sizeof( mbedtls_havege_state ) );
 }
 
 /*