UefiCpuPkg: Extend SMM CPU Service with rendezvous support.

REF? https://bugzilla.tianocore.org/show_bug.cgi?id=3815

This patch define a new Protocol with the new services
SmmWaitForAllProcessor(), which can be used by SMI handler
to optionally wait for other APs to complete SMM rendezvous in
relaxed AP mode.

A new library SmmCpuRendezvousLib is provided to abstract the service
into library API to simple SMI handler code.

Cc: Eric Dong <eric.dong@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Zhihao Li <zhihao.li@intel.com>

Signed-off-by: Zhihao Li <zhihao.li@intel.com>

UefiCpuPkg/Include/Library/SmmCpuRendezvousLib.h

@@ -0,0 +1,27 @@
+/** @file
+  SMM CPU Rendezvous library header file.
+
+  Copyright (c) 2022, Intel Corporation. All rights reserved.<BR>
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef SMM_CPU_RENDEZVOUS_H_
+#define SMM_CPU_RENDEZVOUS_H_
+
+/**
+  This routine wait for all AP processors to arrive in SMM.
+
+  @param[in]  BlockingMode  Blocking mode or non-blocking mode.
+
+  @retval EFI_SUCCESS       All processors checked in to SMM.
+  @retval EFI_TIMEOUT       Wait for all APs until timeout.
+
+**/
+EFI_STATUS
+EFIAPI
+SmmWaitForAllProcessor (
+  IN  BOOLEAN  BlockingMode
+  );
+
+#endif