Tell TF-A in EL3 about TEE message buffers.

This must be enabled by a flag in the manifest, as it won't work without
the matching support in TF-A, e.g. in the case of running tests on QEMU
without TF-A.

Bug: 132429380
Change-Id: I0a0848c7b1afb416d98c0afeabcc4601abf9d193
diff --git a/src/manifest.c b/src/manifest.c
index 438b5d0..9b80106 100644
--- a/src/manifest.c
+++ b/src/manifest.c
@@ -280,6 +280,8 @@
 		return MANIFEST_ERROR_NOT_COMPATIBLE;
 	}
 
+	TRY(read_bool(&hyp_node, "spci_tee", &manifest->spci_tee_enabled));
+
 	/* Iterate over reserved VM IDs and check no such nodes exist. */
 	for (i = 0; i < HF_VM_ID_OFFSET; i++) {
 		spci_vm_id_t vm_id = (spci_vm_id_t)i;