MdeModulePkg: Variable: Introduce MM based variable read service in PEI

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4464

This change introduced the Standalone MM based variable read capability
in PEI phase for applicable platforms (such as ARM platforms).

Similar to the x86 counterpart, MM communicate PPI is used to request
variable information from Standalone MM environment.

Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Jian J Wang <jian.j.wang@intel.com>

Co-authored-by: Ronny Hansen <hansen.ronny@microsoft.com>
Co-authored-by: Shriram Masanamuthu Chinnathurai <shriramma@microsoft.com>
Co-authored-by: Preshit Harlikar <pharlikar@microsoft.com>
Signed-off-by: Kun Qin <kuqin@microsoft.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

MdeModulePkg/Universal/Variable/MmVariablePei/MmVariablePei.inf

@@ -0,0 +1,40 @@
+## @file -- MmVariablePei.inf
+# Provides interface for reading Secure System Variables during PEI.
+#
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+##
+
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = MmVariablePei
+  FILE_GUID                      = CD660A87-454B-4346-A35C-3D89BF8ECFAF
+  MODULE_TYPE                    = PEIM
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = PeiMmVariableInitialize
+
+[Sources]
+  MmVariablePei.c
+  MmVariablePei.h
+
+[Packages]
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+
+[LibraryClasses]
+  PcdLib
+  PeiServicesLib
+  PeimEntryPoint
+  MemoryAllocationLib
+  HobLib
+
+[Protocols]
+  gEfiSmmVariableProtocolGuid             ## CONSUMES
+
+[Ppis]
+  gEfiPeiReadOnlyVariable2PpiGuid         ## PRODUCES
+  gEfiPeiMmCommunicationPpiGuid           ## CONSUMES
+
+[Depex]
+  gEfiPeiMmCommunicationPpiGuid