MdeModulePkg/XhciPei: Support IoMmu.

Update XHCI driver to consume IOMMU_PPI to allocate DMA buffer.

If no IOMMU_PPI exists, this driver still calls PEI service
to allocate DMA buffer, with assumption that DRAM==DMA.

This is a compatible change.

Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Bus/Pci/XhciPei/XhciSched.h

@@ -170,6 +170,7 @@ typedef struct _URB {
   VOID                              *Data;
   UINTN                             DataLen;
   VOID                              *DataPhy;
+  VOID                              *DataMap;
   EFI_ASYNC_USB_TRANSFER_CALLBACK   Callback;
   VOID                              *Context;
   //