OvmfPkg: Refer to Shell app via its declared GUID

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1843

Currently, the file GUID reference of the UEFI Shell app is indirected
via the PCD gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdShellFile,
which is set to a fixed value for OvmfPkg.

So instead, use the symbolic GUID in ShellPkg for this purpose, and drop
the reference to this PCD, and to the IntelFrameworkModulePkg package
entirely.

Cc: Ray Ni <ray.ni@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Hao A Wu <hao.a.wu@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c

@@ -1,7 +1,7 @@
 /** @file
   Platform BDS customizations.
 
-  Copyright (c) 2004 - 2018, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2004 - 2019, Intel Corporation. All rights reserved.<BR>
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -1532,7 +1532,7 @@ PlatformBootManagerAfterConsole (
   // Register UEFI Shell
   //
   PlatformRegisterFvBootOption (
-    PcdGetPtr (PcdShellFile), L"EFI Internal Shell", LOAD_OPTION_ACTIVE
+    &gUefiShellFileGuid, L"EFI Internal Shell", LOAD_OPTION_ACTIVE
     );
 
   RemoveStaleFvFileOptions ();