Build: Exclude mbedTLS targets from all

This patch makes sure that mbedTLS specific targets
are not added by default to the all target. This
allows to avoid installing them by default as they
are not needed/used and allow to build them only
when pulled in as a dependency from other targets.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: Ic1d8f8efdf8a706a2e1d6361fb1c9815e8da711f
diff --git a/bl2/CMakeLists.txt b/bl2/CMakeLists.txt
index 496515b..3cba7ad 100644
--- a/bl2/CMakeLists.txt
+++ b/bl2/CMakeLists.txt
@@ -92,7 +92,7 @@
 # symbols whild optimizing space.
 set(SAVED_BUILD_TYPE ${CMAKE_BUILD_TYPE})
 set(CMAKE_BUILD_TYPE ${MBEDCRYPTO_BUILD_TYPE})
-add_subdirectory(${MBEDCRYPTO_PATH} ${CMAKE_CURRENT_BINARY_DIR}/mbedcrypto)
+add_subdirectory(${MBEDCRYPTO_PATH} ${CMAKE_CURRENT_BINARY_DIR}/mbedcrypto EXCLUDE_FROM_ALL)
 set(CMAKE_BUILD_TYPE ${SAVED_BUILD_TYPE} CACHE STRING "Build type: [Debug, Release, RelWithDebInfo, MinSizeRel]" FORCE)
 
 if(NOT TARGET bl2_mbedcrypto)