EmbeddedPkg: Mark DMA Memory Allocations XP By Default

When allocating memory for a non-coherent DMA device, the current core
code removes the XP attribute, allowing code to execute from that
region. This is a security vulnerability and unneeded. This change
updates to mark the region as XP when allocating memory for the
non-coherent DMA device.

These allocations in this function are limited to `EfiBootServicesData`
and `EfiRuntimeServicesData`, which we expect to be XP.

EmbeddedPkg/Library/NonCoherentDmaLib/NonCoherentDmaLib.c

@@ -557,7 +557,7 @@ DmaAllocateAlignedBuffer (
   Status = gDS->SetMemorySpaceAttributes (
                   (PHYSICAL_ADDRESS)(UINTN)Allocation,
                   EFI_PAGES_TO_SIZE (Pages),
-                  MemType
+                  MemType | EFI_MEMORY_XP // MU_CHANGE: Allocate DMA memory XP by default
                   );
   if (EFI_ERROR (Status)) {
     goto FreeAlloc;