test(tc): centralize platform error handling

Note that this change only affects the platform tests execution
path. It has no impact on the normal boot flow.

Make individual test functions propagate an error code, instead of
calling the platform error handler at the point of failure. The latter
is now the responsibility of the caller - in this case
tc_bl31_common_platform_setup().

Note that right now, tc_bl31_common_platform_setup() does not look at
the said error code but this initial change opens up an opportunity to
centralize any error handling in tc_bl31_common_platform_setup(),
which we will seize in subsequent patches.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: Ib282b64039e0b1ec6e6d29476fbaa2bcd33cb0c7
diff --git a/plat/arm/board/tc/tc_bl31_setup.c b/plat/arm/board/tc/tc_bl31_setup.c
index d2a14d2..ec28f3a 100644
--- a/plat/arm/board/tc/tc_bl31_setup.c
+++ b/plat/arm/board/tc/tc_bl31_setup.c
@@ -59,7 +59,7 @@
 #elif PLATFORM_TEST_TFM_TESTSUITE
 	run_platform_tests();
 #endif
-	/* Suspend booting */
+	/* Suspend booting, no matter the tests outcome. */
 	plat_error_handler(-1);
 #endif
 }