test(tc): test for AP/RSS NV counter interface

Change in PLATFORM_TEST build flag from boolean -> string, with the
current string options being tfm-testsuite and rss-nv-counters.

To get the old behavior, i.e. where we used to use PLATFORM_TEST=1,
we now need to pass PLATFORM_TEST=tfm-testsuite.

Adding new test of the AP/RSS interface for non-volatile counters.
The test reads, increments, and reads again each 3 types of NV
counters for: CCA, secure, and non-secure firmware. Enabled by
PLATFORM_TEST=rss-nv-counters.

Change-Id: I2044cc9b2f37984697e0754c9c824eab51a11e7f
Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/plat/arm/board/tc/include/tc_plat.h b/plat/arm/board/tc/include/tc_plat.h
index f7ce2fe..ba1831f 100644
--- a/plat/arm/board/tc/include/tc_plat.h
+++ b/plat/arm/board/tc/include/tc_plat.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2021-2023, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -11,6 +11,7 @@
 
 #ifdef PLATFORM_TEST
 void run_platform_tests(void);
+void nv_counter_test(void);
 #endif
 
 #endif /* TC_PLAT_H */