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>