MdeModulePkg/PciBus: Add IOMMU support.

If IOMMU protocol is installed, PciBus need call IOMMU
to set access attribute for the PCI device in Map/Ummap.

Only after the access attribute is set, the PCI device can
access the DMA memory.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Leo Duran <leo.duran@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Previous patch Tested-by: Brijesh Singh <brijesh.singh@amd.com>
Previous patch Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Leo Duran <leo.duran@amd.com>

MdeModulePkg/Bus/Pci/PciBusDxe/PciBus.c

@@ -42,6 +42,7 @@ UINT64                                        gAllZero             = 0;
 
 EFI_PCI_PLATFORM_PROTOCOL                     *gPciPlatformProtocol;
 EFI_PCI_OVERRIDE_PROTOCOL                     *gPciOverrideProtocol;
+EDKII_IOMMU_PROTOCOL                          *mIoMmuProtocol;
 
 
 GLOBAL_REMOVE_IF_UNREFERENCED EFI_PCI_HOTPLUG_REQUEST_PROTOCOL mPciHotPlugRequest = {
@@ -284,6 +285,14 @@ PciBusDriverBindingStart (
           );
   }  
 
+  if (mIoMmuProtocol == NULL) {
+    gBS->LocateProtocol (
+          &gEdkiiIoMmuProtocolGuid,
+          NULL,
+          (VOID **) &mIoMmuProtocol
+          );
+  }
+
   if (PcdGetBool (PcdPciDisableBusEnumeration)) {
     gFullEnumeration = FALSE;
   } else {