MdePkg/BaseLib: BaseLib for RISCV64 architecture

Add RISC-V RV64 BaseLib functions.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2672

Signed-off-by: Abner Chang <abner.chang@hpe.com>
Co-authored-by: Gilbert Chen <gilbert.chen@hpe.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Zhiguang Liu <zhiguang.liu@intel.com>

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Gilbert Chen <gilbert.chen@hpe.com>

MdePkg/Library/BaseLib/RiscV64/CpuPause.c

@@ -0,0 +1,29 @@
+/** @file
+  CPU pause for RISC-V
+
+  Copyright (c) 2020, Hewlett Packard Enterprise Development LP. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include "BaseLibInternals.h"
+
+extern VOID RiscVCpuPause (VOID);
+
+
+/**
+  Requests CPU to pause for a short period of time.
+
+  Requests CPU to pause for a short period of time. Typically used in MP
+  systems to prevent memory starvation while waiting for a spin lock.
+
+**/
+VOID
+EFIAPI
+CpuPause (
+  VOID
+  )
+{
+  RiscVCpuPause ();
+}
+