Implement SPCI_RX_RELEASE to replace hf_mailbox_clear.

Bug: 132421502
Change-Id: I63ffcce9b998ef98ff7ec3cdef41415a56a91b9f
diff --git a/inc/hf/api.h b/inc/hf/api.h
index 1854e9f..91f02b2 100644
--- a/inc/hf/api.h
+++ b/inc/hf/api.h
@@ -30,7 +30,6 @@
 void api_regs_state_saved(struct vcpu *vcpu);
 int64_t api_vm_configure(ipaddr_t send, ipaddr_t recv, struct vcpu *current,
 			 struct vcpu **next);
-int64_t api_mailbox_clear(struct vcpu *current, struct vcpu **next);
 int64_t api_mailbox_writable_get(const struct vcpu *current);
 int64_t api_mailbox_waiter_get(spci_vm_id_t vm_id, const struct vcpu *current);
 int64_t api_share_memory(spci_vm_id_t vm_id, ipaddr_t addr, size_t size,
@@ -55,6 +54,7 @@
 				    struct vcpu **next);
 struct spci_value api_spci_msg_recv(bool block, struct vcpu *current,
 				    struct vcpu **next);
+struct spci_value api_spci_rx_release(struct vcpu *current, struct vcpu **next);
 void api_yield(struct vcpu *current, struct vcpu **next);
 struct spci_value api_spci_version(void);
 struct spci_value api_spci_id_get(const struct vcpu *current);