Move the one non-crypto-specific PSA helper macro to a new header

Create a new header file psa_helpers.h and put the one helper macro
that isn't specific to PSA crypto there. Use this header file in the
ITS test suite.
diff --git a/tests/Makefile b/tests/Makefile
index e2a32a1..52f9163 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -105,6 +105,7 @@
 	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) $<	$(LOCAL_LDFLAGS) $(LDFLAGS) -o $@
 
 $(filter test_suite_psa_crypto%, $(BINARIES)): psa_crypto_helpers.h
+$(filter test_suite_psa_%, $(BINARIES)): psa_helpers.h
 
 clean:
 ifndef WINDOWS