ArmPkg/ArmMmuLib: Use function pointer type

mReplaceLiveEntryFunc is a function pointer but assigned as a VOID*
pointer:

  mReplaceLiveEntryFunc = *(VOID **)GET_GUID_HOB_DATA (Hob);

This leads to the Visual Studio warning:

  nonstandard extension, function/data pointer conversion in
  expression

This change updates the assignment to avoid using a data pointer and
defines a type for the function pointer to succinctly and accurately
refer to the type when it is used in the library code.

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

ArmPkg/Library/ArmMmuLib/ArmMmuLibInternal.h

@@ -0,0 +1,23 @@
+/** @file
+  Arm MMU library instance internal header file.
+
+  Copyright (C) Microsoft Corporation. All rights reserved.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef ARM_MMU_LIB_INTERNAL_H_
+#define ARM_MMU_LIB_INTERNAL_H_
+
+typedef
+VOID(
+ EFIAPI  *ARM_REPLACE_LIVE_TRANSLATION_ENTRY
+ )(
+  IN  UINT64  *Entry,
+  IN  UINT64  Value,
+  IN  UINT64  RegionStart,
+  IN  BOOLEAN DisableMmu
+  );
+
+#endif