Hide switch to primary logic.

This should not be called directly by arch code.

Change-Id: I8a83179d66565e571ff4a4b254020af4a06a937b
diff --git a/src/arch/aarch64/handler.c b/src/arch/aarch64/handler.c
index 538c3b3..88aaf38 100644
--- a/src/arch/aarch64/handler.c
+++ b/src/arch/aarch64/handler.c
@@ -214,8 +214,7 @@
 	/* TODO: Only switch if we know the interrupt was not for the secondary
 	 * VM. */
 	/* Switch back to primary VM, interrupts will be handled there. */
-	return api_switch_to_primary(HF_VCPU_RUN_RESPONSE(HF_VCPU_RUN_YIELD, 0),
-				     vcpu_state_ready);
+	return api_yield();
 }
 
 struct vcpu *sync_lower_exception(uint64_t esr)