MdePkg/BaseRngLib: Add support for ARMv8.5 RNG instructions

Make BaseRngLib more generic by moving x86-specific functionality into
'Rand' and adding files under 'AArch64' to support the optional ARMv8.5
RNG instruction RNDR that is a part of FEAT_RNG.

Signed-off-by: Rebecca Cran <rebecca@nuviainc.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

MdePkg/Library/BaseRngLib/AArch64/ArmReadIdIsar0.asm

@@ -0,0 +1,30 @@
+;------------------------------------------------------------------------------
+;
+; ArmReadIdIsar0() for AArch64
+;
+; Copyright (c) 2021, NUVIA Inc. All rights reserved.<BR>
+;
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+;------------------------------------------------------------------------------
+
+  EXPORT ArmReadIdIsar0
+  AREA BaseLib_LowLevel, CODE, READONLY
+
+;/**
+;  Reads the ID_AA64ISAR0 Register.
+;
+; @return The contents of the ID_AA64ISAR0 register.
+;
+;**/
+;UINT64
+;EFIAPI
+;ArmReadIdIsar0 (
+;  VOID
+;  );
+;
+ArmReadIdIsar0
+  mrs  x0, id_aa64isar0_el1 // Read ID_AA64ISAR0 Register
+  ret
+
+  END