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.S

@@ -0,0 +1,31 @@
+#------------------------------------------------------------------------------
+#
+# ArmReadIdIsar0() for AArch64
+#
+# Copyright (c) 2021, NUVIA Inc. All rights reserved.<BR>
+#
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+#------------------------------------------------------------------------------
+
+.text
+.p2align 2
+GCC_ASM_EXPORT(ArmReadIdIsar0)
+
+#/**
+#  Reads the ID_AA64ISAR0 Register.
+#
+#  @return The contents of the ID_AA64ISAR0 register.
+#
+#**/
+#UINT64
+#EFIAPI
+#ArmReadIdIsar0 (
+#  VOID
+#  );
+#
+ASM_PFX(ArmReadIdIsar0):
+  mrs  x0, id_aa64isar0_el1 // Read ID_AA64ISAR0 Register
+  ret
+
+