fixed DMA not be stopped issue when gBS->ExitBootServices called.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@8058 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Bus/Pci/EhciDxe/Ehci.h

@@ -22,6 +22,8 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 #include <Protocol/Usb2HostController.h>
 #include <Protocol/PciIo.h>
 
+#include <Guid/EventGroup.h>
+
 #include <Library/DebugLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/UefiDriverEntryPoint.h>
@@ -120,6 +122,12 @@ struct _USB2_HC_DEV {
   EHC_QTD                  *ShortReadStop;
   EFI_EVENT                 PollTimer;
 
+  //
+  // ExitBootServicesEvent is used to stop the EHC DMA operation 
+  // after exit boot service.
+  //
+  EFI_EVENT                 ExitBootServiceEvent;
+
   //
   // Asynchronous(bulk and control) transfer schedule data:
   // ReclaimHead is used as the head of the asynchronous transfer