Migrate to threading_helpers.h

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index 86ff5b4..b5f5796 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -8,6 +8,7 @@
 #include <test/random.h>
 #include <test/bignum_helpers.h>
 #include <test/psa_crypto_helpers.h>
+#include <test/threading_helpers.h>
 
 #include <errno.h>
 #include <limits.h>