SPCI: SPCI_YIELD.

Adapted hf_vcpu_yield to conform with the spci_yield specification.

Change-Id: I7ad11e83f068a09a19fd930dcead787b5a22e498
diff --git a/inc/hf/api.h b/inc/hf/api.h
index c63f95c..75a85e2 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -40,7 +40,6 @@
 
 struct vcpu *api_preempt(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);
@@ -53,3 +52,4 @@
 			  struct vcpu **next);
 int32_t api_spci_msg_recv(uint32_t attributes, struct vcpu *current,
 			  struct vcpu **next);
+int32_t api_spci_yield(struct vcpu *current, struct vcpu **next);