fix: build dependency in test-realms-payload

The patch [1] refactored the SPM testing code to
reorganise the build for aarch32 of SPM test code.

This broke a dependency of host_realm_spm.c.
This patch uses the source file that was created in [1]
to provide the necessary dependency.

[1] https://review.trustedfirmware.org/c/TF-A/tf-a-tests/+/22272

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I07885cbfee18810610bd2c42d399de77ef2352c1
diff --git a/tftf/tests/tests-realm-payload.mk b/tftf/tests/tests-realm-payload.mk
index 0e0d148..ee8ebc0 100644
--- a/tftf/tests/tests-realm-payload.mk
+++ b/tftf/tests/tests-realm-payload.mk
@@ -29,6 +29,7 @@
 		${ARCH}/ffa_arch_helpers.S				\
 		ffa_helpers.c						\
 		spm_common.c						\
+		spm_test_helpers.c					\
 	)
 
 TESTS_SOURCES	+=							\