MdeModulePkg/Capsule: Remove RT restriction in UpdateCapsule service.

Current UpdateCapsule service will reject all non-reset capsule images and
return EFI_OUT_OF_RESOURCE if the system is at runtime. This will block a
platform CapsuleLib from implementing ProcessCapsuleImage() with runtime
capsule processing capability.

This patch removes this restriction. The change is controled by a feature
PCD PcdSupportProcessCapsuleAtRuntime, and the default value is FALSE
which means not enable this feature.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2501

Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Signed-off-by: Siyuan Fu <siyuan.fu@intel.com>

MdeModulePkg/Universal/CapsuleRuntimeDxe/CapsuleRuntimeDxe.inf

@@ -4,7 +4,7 @@
 #  It installs the Capsule Architectural Protocol defined in PI1.0a to signify
 #  the capsule runtime services are ready.
 #
-#  Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2006 - 2020, Intel Corporation. All rights reserved.<BR>
 #  SPDX-License-Identifier: BSD-2-Clause-Patent
 #
 ##
@@ -82,7 +82,8 @@
   gEdkiiVariableLockProtocolGuid
 
 [FeaturePcd]
-  gEfiMdeModulePkgTokenSpaceGuid.PcdSupportUpdateCapsuleReset   ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSupportUpdateCapsuleReset        ## CONSUMES
+  gEfiMdeModulePkgTokenSpaceGuid.PcdSupportProcessCapsuleAtRuntime   ## CONSUMES
 
 [FeaturePcd.X64]
   gEfiMdeModulePkgTokenSpaceGuid.PcdDxeIplSwitchToLongMode      ## CONSUMES