ShellPkg/acpiview: GTDT updates for ACPI 6.3

The ACPI 6.3 specification introduces support to describe
the ARMv8.1 virtual EL2 timers. This patch updates the GTDT parser
of acpiview to decode the EL2 virtual timer fields.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>

ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Gtdt/GtdtParser.c

@@ -5,7 +5,7 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
   @par Reference(s):
-    - ACPI 6.2 Specification - Errata A, September 2017
+    - ACPI 6.3 Specification - January 2019
   **/
 
 #include <IndustryStandard/Acpi.h>
@@ -77,7 +77,9 @@ STATIC CONST ACPI_PARSER GtdtParser[] = {
   {L"Platform Timer Count", 4, 88, L"%d", NULL,
    (VOID**)&GtdtPlatformTimerCount, NULL, NULL},
   {L"Platform Timer Offset", 4, 92, L"0x%x", NULL,
-   (VOID**)&GtdtPlatformTimerOffset, NULL, NULL}
+   (VOID**)&GtdtPlatformTimerOffset, NULL, NULL},
+  {L"Virtual EL2 Timer GSIV", 4, 96, L"0x%x", NULL, NULL, NULL, NULL},
+  {L"Virtual EL2 Timer Flags", 4, 100, L"0x%x", NULL, NULL, NULL, NULL}
 };
 
 /**