test(nop): add "nop" test case

This is intended for use in conjunction with Trusted Firmware eXplorer
(TFX). The dummy test case exists only to provide a symbol with a
well-known name ("debug_hook"), at which TFX can set a breakpoint and
therefore marshall all PEs on entry to Non-secure state.

The "nop" test case is not built by default, and therefore must be
explicitly included, e.g.

    make TESTS=nop

Signed-off-by: Gareth Stockwell <gareth.stockwell@arm.com>
Change-Id: I1d0f95714e5f662ca0f2d90db32020be15b43aed
diff --git a/tftf/tests/tests-nop.mk b/tftf/tests/tests-nop.mk
new file mode 100644
index 0000000..0cad482
--- /dev/null
+++ b/tftf/tests/tests-nop.mk
@@ -0,0 +1,9 @@
+#
+# Copyright (c) 2023, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+TESTS_SOURCES	+=	$(addprefix tftf/tests/misc_tests/,	\
+				test_nop.c	 		\
+			)