Move back timing.c to mbedtls

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/programs/x509/CMakeLists.txt b/programs/x509/CMakeLists.txt
index 1c91461..c3ee348 100644
--- a/programs/x509/CMakeLists.txt
+++ b/programs/x509/CMakeLists.txt
@@ -20,6 +20,8 @@
 endforeach()
 
 target_link_libraries(cert_app ${mbedtls_target})
+# For mbedtls_timing_get_timer()
+target_link_libraries(load_roots ${mbedtls_target})
 
 install(TARGETS ${executables}
         DESTINATION "bin"