Make yield a noop for the primary.

Change-Id: Idc5f650928eef5185dfa604a52f2a580acaf514a
diff --git a/inc/hf/api.h b/inc/hf/api.h
index 06f33fd..95d97ab 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -43,8 +43,8 @@
 			 enum hf_share share, struct vcpu *current);
 
 struct vcpu *api_preempt(struct vcpu *current);
-struct vcpu *api_yield(struct vcpu *current);
 struct vcpu *api_wait_for_interrupt(struct vcpu *current);
+struct vcpu *api_yield(struct vcpu *current);
 struct vcpu *api_abort(struct vcpu *current);
 
 int64_t api_interrupt_enable(uint32_t intid, bool enable, struct vcpu *current);