Add mbedtls_platform_memmove() as a secured memcmp()

Signed-off-by: Piotr Nowicki <piotr.nowicki@arm.com>
diff --git a/include/mbedtls/platform_util.h b/include/mbedtls/platform_util.h
index fa9f326..d05c3c7 100644
--- a/include/mbedtls/platform_util.h
+++ b/include/mbedtls/platform_util.h
@@ -199,6 +199,22 @@
 void *mbedtls_platform_memcpy( void *dst, const void *src, size_t num );
 
 /**
+ * \brief       Secure memmove
+ *
+ *              This is a constant-time version of memmove(). It is based on
+ *              the double use of the mbedtls_platform_memcpy() function secured
+ *              against side-channel attacks.
+ *
+ * \param dst   Destination buffer where the data is being moved to.
+ * \param src   Source buffer where the data is being moved from.
+ * \param num   The length of the buffers in bytes.
+ *
+ * \return      0 if the operation was successful or -1 if memory allocation
+ *              failed.
+ */
+int mbedtls_platform_memmove( void *dst, const void *src, size_t num );
+
+/**
  * \brief       Secure memcmp
  *
  *              This is a constant-time version of memcmp(). If