ArmPkg/ArmHvcLibNull: Add NULL instance of ArmHvcLib

Add a Null instance of ArmHvcLib in case of library dependencies.

Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>

ArmPkg/ArmPkg.dsc

@@ -132,6 +132,7 @@
   ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.inf
 
   ArmPkg/Library/ArmHvcLib/ArmHvcLib.inf
+  ArmPkg/Library/ArmHvcLibNull/ArmHvcLibNull.inf
   ArmPkg/Library/ArmMonitorLib/ArmMonitorLib.inf
   ArmPkg/Library/ArmSmcLib/ArmSmcLib.inf
   ArmPkg/Library/ArmSmcLibNull/ArmSmcLibNull.inf

ArmPkg/Library/ArmHvcLibNull/ArmHvcLibNull.c

@@ -0,0 +1,29 @@
+/** @file
+  Arm HyperVisor Call (HVC) Null Library.
+
+  Copyright (c) 2022, Arm Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Library/ArmHvcLib.h>
+#include <Library/DebugLib.h>
+
+/**
+  Trigger an HVC call
+
+  HVC calls can take up to 8 arguments and return up to 4 return values.
+  Therefore, the 4 first fields in the ARM_HVC_ARGS structure are used
+  for both input and output values.
+
+  @param [in,out]  Args    Arguments for the HVC call.
+**/
+VOID
+ArmCallHvc (
+  IN OUT ARM_HVC_ARGS  *Args
+  )
+{
+  ASSERT (FALSE);
+  return;
+}

ArmPkg/Library/ArmHvcLibNull/ArmHvcLibNull.inf

@@ -0,0 +1,22 @@
+## @file
+#  Arm Hvc Null Library
+#
+#  Copyright (c) 2022, Arm Limited. All rights reserved.<BR>
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+##
+
+[Defines]
+  INF_VERSION                    = 1.29
+  BASE_NAME                      = ArmHvcLibNull
+  FILE_GUID                      = 02076A46-D6DB-48DD-8E5F-153172DD73A1
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = ArmHvcLib
+
+[Sources]
+  ArmHvcLibNull.c
+
+[Packages]
+  ArmPkg/ArmPkg.dec
+  MdePkg/MdePkg.dec