MdeModulePkg/CapsuleRuntimeDxe: Add cache flush for IA32 and X64

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1462

The IA32 and X64 ARCH need cache flush function during capsule update.
And the cache flush is already implemented in arm ARCH, so add this
function CapsuleCacheWriteBack() to IA32 and X64 ARCH. And add a null
version for EBC.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdeModulePkg/Universal/CapsuleRuntimeDxe/CapsuleReset.c

@@ -3,6 +3,7 @@
   PersistAcrossReset capsules
 
   Copyright (c) 2018, Linaro, Ltd. All rights reserved.<BR>
+  Copyright (c) 2019, 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 which accompanies this
@@ -32,18 +33,3 @@ IsPersistAcrossResetCapsuleSupported (
   return FeaturePcdGet (PcdSupportUpdateCapsuleReset);
 }
 
-/**
-  Writes Back a range of data cache lines covering a set of capsules in memory.
-
-  Writes Back the data cache lines specified by ScatterGatherList.
-
-  @param  ScatterGatherList Physical address of the data structure that
-                            describes a set of capsules in memory
-
-**/
-VOID
-CapsuleCacheWriteBack (
-  IN  EFI_PHYSICAL_ADDRESS    ScatterGatherList
-  )
-{
-}