Build: Split NS and Secure regression tests build

Seperate NS and Secure regressin test builds.

  - TF-M secure build integrates secure regression tests and test
    services via test/secure_regression.
  - Non-secure regression tests are built via test/ns_regression.
  - Pass tf-m-tests test config to TF-M secure build via argument
    CONFIG_TFM_TEST_CONFIG_FILE.
  - Fix issues when no regression test is enabled.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I1e550bf6d6a36a220275743c3312a61f7ae2c78e
diff --git a/tests_reg/test_app.c b/tests_reg/test_app.c
index bd45b38..d29743c 100644
--- a/tests_reg/test_app.c
+++ b/tests_reg/test_app.c
@@ -7,7 +7,9 @@
 
 #include "test_app.h"
 #include "tfm_log.h"
+#ifdef TFM_NS_REG_TEST
 #include "test_framework_integ_test.h"
+#endif
 
 /**
  * \brief Services test thread
@@ -18,7 +20,9 @@
 {
     UNUSED_VARIABLE(argument);
 
+#ifdef TFM_NS_REG_TEST
     tfm_non_secure_client_run_tests();
+#endif
 
     /* Output EOT char for test environments like FVP. */
     LOG_MSG("\x04");