ArmPkg/ArmLib: add ArmHasGicSystemRegisters () helper function

Create a helper function to eliminate direct feature register reading,
which gets messy in code shared between ARM/AArch64.

Returns BOOLEAN True if the CPU implements the GIC System Register
Interface (any version), otherwise returns BOOL False.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

ArmPkg/Library/ArmLib/AArch64/AArch64Lib.c

@@ -2,6 +2,7 @@
 
   Copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>
   Portions copyright (c) 2011 - 2014, ARM Ltd. All rights reserved.<BR>
+  Copyright (c) 2020, NUVIA Inc. All rights reserved.<BR>
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
@@ -71,3 +72,18 @@ ArmCleanDataCache (
   ArmDataSynchronizationBarrier ();
   AArch64DataCacheOperation (ArmCleanDataCacheEntryBySetWay);
 }
+
+/**
+  Check whether the CPU supports the GIC system register interface (any version)
+
+  @return   Whether GIC System Register Interface is supported
+
+**/
+BOOLEAN
+EFIAPI
+ArmHasGicSystemRegisters (
+  VOID
+  )
+{
+  return ((ArmReadIdPfr0 () & AARCH64_PFR0_GIC) != 0);
+}