Change FF-A UUID manipulation method before sending to Hafnium (#343)

## Description

There is a mismatch between the FF-A spec definition, UEFI definition
and the code implementation.

This UUID manipulation just changes the mangling method that matches the
FF-A UUID mangling method before ARM made it public. Because everybody
else is using this way...

For details on how to complete these options and their meaning refer to
[CONTRIBUTING.md](https://github.com/microsoft/mu/blob/HEAD/CONTRIBUTING.md).

- [x] Impacts functionality?
- [ ] Impacts security?
- [ ] Breaking change?
- [ ] Includes tests?
- [ ] Includes documentation?
- [ ] Backport to release branch?

## How This Was Tested

This was tested on proprietary hardware and QEMU SBSA virtual platform.

## Integration Instructions

N/A

---------

Signed-off-by: Kun Qin <kun.qin@microsoft.com>

ArmPkg/Library/ArmFfaLib/ArmFfaCommon.c

@@ -66,12 +66,21 @@ ConvertEfiGuidToUuid (
   UINT32  *Data32;
   UINT16  *Data16;
 
+  // MU_CHANGE Starts: Update UUID mangling method
+  if ((Guid == NULL) || (Uuid == NULL)) {
+    return;
+  }
+  // MU_CHANGE Ends
+
   CopyGuid ((EFI_GUID *)Uuid, Guid);
-  Data32    = (UINT32 *)Uuid;
-  Data32[0] = SwapBytes32 (Data32[0]);
+  Data32 = (UINT32 *)Uuid;
+  // Data32[0] = SwapBytes32 (Data32[0]); // MU_CHANGE Starts: Update UUID mangling method
   Data16    = (UINT16 *)&Data32[1];
+  Data32[1] = SwapBytes32 (Data32[1]); // MU_CHANGE: Update UUID mangling method
   Data16[0] = SwapBytes16 (Data16[0]);
   Data16[1] = SwapBytes16 (Data16[1]);
+  Data32[2] = SwapBytes32 (Data32[2]); // MU_CHANGE: Update UUID mangling method
+  Data32[3] = SwapBytes32 (Data32[3]); // MU_CHANGE: Update UUID mangling method
 }
 
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