xen_pt: Fix passthrough of device with ROM.

QEMU does not need and should not allocate memory for the ROM of a
passthrough PCI device. So this patch initialize the particular region
like any other PCI BAR of a passthrough device.

When a guest will access the ROM, Xen will take care of the IO, QEMU
will not be involved in it.

Xen set a limit of memory available for each guest, allocating memory
for a ROM can hit this limit.
Signed-off-by: NAnthony PERARD <anthony.perard@citrix.com>
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Reported-and-Tested-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

hw/xen/xen_pt.c

@@ -440,8 +440,8 @@ static int xen_pt_register_regions(XenPCIPassthroughState *s)
 
         s->bases[PCI_ROM_SLOT].access.maddr = d->rom.base_addr;
 
-        memory_region_init_rom_device(&s->rom, OBJECT(s), NULL, NULL,
-                                      "xen-pci-pt-rom", d->rom.size);
+        memory_region_init_io(&s->rom, OBJECT(s), &ops, &s->dev,
+                              "xen-pci-pt-rom", d->rom.size);
         pci_register_bar(&s->dev, PCI_ROM_SLOT, PCI_BASE_ADDRESS_MEM_PREFETCH,
                          &s->rom);