Create a library file for libmbedtls

TF Makefile was linking all the objects files generated for the
Mbed TLS library instead of creating a static library that could be
used in the linking stage.

Change-Id: I8e4cd843ef56033c9d3faeee71601d110b7e4c12
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/bl2/bl2.mk b/bl2/bl2.mk
index a856fb7..7e33703 100644
--- a/bl2/bl2.mk
+++ b/bl2/bl2.mk
@@ -8,9 +8,7 @@
 				bl2/${ARCH}/bl2_arch_setup.c		\
 				lib/locks/exclusive/${ARCH}/spinlock.S	\
 				plat/common/${ARCH}/platform_up_stack.S	\
-				${MBEDTLS_COMMON_SOURCES}               \
-				${MBEDTLS_CRYPTO_SOURCES}		\
-				${MBEDTLS_X509_SOURCES}
+				${MBEDTLS_SOURCES}
 
 ifeq (${ARCH},aarch64)
 BL2_SOURCES		+=	common/aarch64/early_exceptions.S