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/Include/Library/ArmLib.h

@@ -2,6 +2,7 @@
 
   Copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR>
   Copyright (c) 2011 - 2016, ARM Ltd. All rights reserved.<BR>
+  Copyright (c) 2020, NUVIA Inc. All rights reserved.<BR>
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
@@ -715,4 +716,21 @@ ArmGetPhysicalAddressBits (
   VOID
   );
 
+
+///
+///  ID Register Helper functions
+///
+
+/**
+  Check whether the CPU supports the GIC system register interface (any version)
+
+  @return   Whether GIC System Register Interface is supported
+
+**/
+BOOLEAN
+EFIAPI
+ArmHasGicSystemRegisters (
+  VOID
+  );
+
 #endif // __ARM_LIB__