Make AARCH64 FlatPageTableLib Compilable with MSVC (#476)

## Description

MSVC does not allow inline Assembly, so some logic which reads an ARM
register needed to be moved to a separate nasm file:
https://learn.microsoft.com/en-us/cpp/assembler/inline/inline-assembler?view=msvc-170

- [x] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

Tested by building the module with MSVC

## Integration Instructions

N/A

UefiTestingPkg/Library/FlatPageTableLib/AArch64/FlatPageTableAArch64.c

@@ -73,6 +73,20 @@ typedef union {
 
 STATIC BOOLEAN  mHierarchicalControlEnabled = FALSE;
 
+#if !defined (__clang__) && !defined (__GNUC__)
+
+/**
+  Reads the ID_AA64MMFR1_EL1 special register.
+
+  @retval The UINT64 value of the ID_AA64MMFR1_EL1 special register.
+**/
+UINT64
+Asm_Read_ID_AA64MMFR1_EL1 (
+  VOID
+  );
+
+#else
+
 /**
   Reads the ID_AA64MMFR1_EL1 special register.
 
@@ -90,6 +104,8 @@ Asm_Read_ID_AA64MMFR1_EL1 (
   return value;
 }
 
+#endif
+
 /**
   Checks the ID_AA64MMFR1_EL1 and TCR special registers to see if hierarchical control is enabled.
 

UefiTestingPkg/Library/FlatPageTableLib/AArch64/ReadIdMmfr1.asm

@@ -0,0 +1,23 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (c) Microsoft Corporation. All rights reserved.
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;------------------------------------------------------------------------------
+
+    EXPORT Asm_Read_ID_AA64MMFR1_EL1
+    AREA |.text|, CODE, READONLY
+
+;------------------------------------------------------------------------------
+; Reads the ID_AA64MMFR1_EL1 special register.
+;
+; @retval The UINT64 value of the ID_AA64MMFR1_EL1 special register.
+;
+; UINT64
+; Asm_Read_ID_AA64MMFR1_EL1 (
+;   VOID
+;   );
+;------------------------------------------------------------------------------
+Asm_Read_ID_AA64MMFR1_EL1
+    MRS X0, ID_AA64MMFR1_EL1
+    RET
+    END

UefiTestingPkg/Library/FlatPageTableLib/FlatPageTableLib.inf

@@ -32,6 +32,7 @@
 
 [Sources.AARCH64]
   AArch64/FlatPageTableAArch64.c
+  AArch64/ReadIdMmfr1.asm | MSFT
 
 [Packages]
   MdePkg/MdePkg.dec