OvmfPkg/VirtioGpuDxe: take EFI_PHYSICAL_ADDRESS in ResourceAttachBacking()

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 4b725858de68 ("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>