OvmfPkg/VirtioGpuDxe: take EFI_PHYSICAL_ADDRESS in ResourceAttachBacking()

The RESOURCE_ATTACH_BACKING virtio GPU command assigns guest-side backing
pages to a host-side resource that was created earlier with the
RESOURCE_CREATE_2D command.

We compose the RESOURCE_ATTACH_BACKING command in the
VirtioGpuResourceAttachBacking() function. Currently this function takes
the parameter

  IN VOID *FirstBackingPage

This is only appropriate as long as we pass a (guest-phys) system memory
address to the device. In preparation for a mapped bus master device
address, change the above parameter to

  IN EFI_PHYSICAL_ADDRESS BackingStoreDeviceAddress

In order to keep the current call site functional, move the (VOID*) to
(UINTN) conversion out of the function, to the call site.

The "Request.Entry.Addr" field already has type UINT64.

This patch is similar to commit 4b725858de ("OvmfPkg/VirtioLib: change
the parameter of VirtioAppendDesc() to UINT64", 2017-08-23).

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Brijesh Singh <brijesh.singh@amd.com>

OvmfPkg/VirtioGpuDxe/Gop.c

@@ -313,10 +313,10 @@ GopSetMode (
   // Attach backing store to the host resource.
   //
   Status = VirtioGpuResourceAttachBacking (
-             VgpuGop->ParentBus, // VgpuDev
-             NewResourceId,      // ResourceId
-             NewBackingStore,    // FirstBackingPage
-             NewNumberOfPages    // NumberOfPages
+             VgpuGop->ParentBus,           // VgpuDev
+             NewResourceId,                // ResourceId
+             (UINTN)NewBackingStore,       // BackingStoreDeviceAddress
+             NewNumberOfPages              // NumberOfPages
              );
   if (EFI_ERROR (Status)) {
     goto FreeBackingStore;