ArmPkg/CpuDxe: set DmaBufferAlignment according to CWG

The DmaBufferAlignment currently defaults to 4, which is dangerously
small and may result in lost data on platforms that perform non-coherent
DMA. So instead, take the CWG value from the cache info registers.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

ArmPkg/Drivers/CpuDxe/CpuDxe.c

@@ -225,9 +225,18 @@ EFI_CPU_ARCH_PROTOCOL mCpu = {
   CpuGetTimerValue,
   CpuSetMemoryAttributes,
   0,          // NumberOfTimers
-  4,          // DmaBufferAlignment
+  2048,       // DmaBufferAlignment
 };
 
+STATIC
+VOID
+InitializeDma (
+  IN OUT  EFI_CPU_ARCH_PROTOCOL   *CpuArchProtocol
+  )
+{
+  CpuArchProtocol->DmaBufferAlignment = ArmCacheWritebackGranule ();
+}
+
 EFI_STATUS
 CpuDxeInitialize (
   IN EFI_HANDLE         ImageHandle,
@@ -239,6 +248,8 @@ CpuDxeInitialize (
 
   InitializeExceptions (&mCpu);
 
+  InitializeDma (&mCpu);
+
   Status = gBS->InstallMultipleProtocolInterfaces (
                 &mCpuHandle,
                 &gEfiCpuArchProtocolGuid,           &mCpu,