MdePkg/BaseCacheMaintenanceLibNull: Add Null instance for host testing

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2799

The services in CacheMaintenanceLib usually generate exceptions in a
unit test host application.  Provide a Null instance that can be safely
used.

This Null instance can also be used as a template for implementing
new instances of CacheMaintenanceLib.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Library/BaseCacheMaintenanceLibNull/BaseCacheMaintenanceLibNull.inf

@@ -0,0 +1,29 @@
+## @file
+#  Null Cache Maintenance Library implementation.
+#
+#  Copyright (c) 2020, Intel Corporation. All rights reserved.<BR>
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = BaseCacheMaintenanceLibNull
+  MODULE_UNI_FILE                = BaseCacheMaintenanceLibNull.uni
+  FILE_GUID                      = 13F13249-AC31-4373-8B2B-AFC5755A6FCD
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.1
+  LIBRARY_CLASS                  = CacheMaintenanceLib
+
+#
+#  VALID_ARCHITECTURES           = IA32 X64 EBC ARM AARCH64
+#
+
+[Sources]
+  BaseCacheMaintenanceLibNull.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  DebugLib