MdePkg: Add new definitions for Management Mode.

In PI 1.5 version, system management mode name(SMM) has been changed
to Management Mode(MM). It impacts the current code which still use
SMM/Smram/SMI keywords. This patch add new definition which use
MM/MmRam/MMI keywords to follow new spec definitions.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Include/PiMm.h

@@ -0,0 +1,25 @@
+/** @file
+
+  Root include file for Mde Package MM modules.
+
+Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>
+This program and the accompanying materials are licensed and made available under
+the terms and conditions of the BSD License that accompanies this distribution.
+The full text of the license may be found at
+http://opensource.org/licenses/bsd-license.php.
+
+THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#ifndef __PI_MM_H__
+#define __PI_MM_H__
+
+#include <Uefi/UefiBaseType.h>
+#include <Uefi/UefiSpec.h>
+
+#include <Pi/PiMmCis.h>
+
+#endif
+