SPCI: SPCI_YIELD.

Adapted hf_vcpu_yield to conform with the spci_yield specification.

Change-Id: I7ad11e83f068a09a19fd930dcead787b5a22e498
diff --git a/test/hftest/hftest_service.c b/test/hftest/hftest_service.c
index 1278617..5b9fafb 100644
--- a/test/hftest/hftest_service.c
+++ b/test/hftest/hftest_service.c
@@ -114,7 +114,7 @@
 	ctx->memory_size = memory_size;
 
 	/* Pause so the next time cycles are given the service will be run. */
-	hf_vcpu_yield();
+	spci_yield();
 
 	/* Let the service run. */
 	service();