Move to mbedtls-2.10.0 tag

To build with the new release, we pick couple of more files from mbedTLS
library.

Change-Id: I77dfe5723284cb26d4e5c717fb0e6f6dd803cb6b
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

docs/user-guide.rst

@@ -1074,7 +1074,7 @@ images with support for these features:
    is important to use a version that is compatible with TF-A and fixes any
    known security vulnerabilities. See `mbed TLS Security Center`_ for more
    information. The latest version of TF-A is tested with tag
-   ``mbedtls-2.6.0``.
+   ``mbedtls-2.10.0``.
 
    The ``drivers/auth/mbedtls/mbedtls_*.mk`` files contain the list of mbed TLS
    source files the modules depend upon.

drivers/auth/mbedtls/mbedtls_common.mk

 #
-# Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -27,6 +27,8 @@ MBEDTLS_COMMON_SOURCES	:=	drivers/auth/mbedtls/mbedtls_common.c	\
 				memory_buffer_alloc.c			\
 				oid.c 					\
 				platform.c 				\
+				platform_util.c				\
+				rsa_internal.c				\
 				)
 
 endif