hw/virtio-pci Added counter for pcie capabilities offsets.

Removed hardcoded offset for ats. Added cap offset counter
for future capabilities like AER.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
Message-Id: <20201203110713.204938-2-andrew@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -1798,6 +1798,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
 
     if (pcie_port && pci_is_express(pci_dev)) {
         int pos;
+        uint16_t last_pcie_cap_offset = PCI_CONFIG_SPACE_SIZE;
 
         pos = pcie_endpoint_cap_init(pci_dev, 0);
         assert(pos > 0);
@@ -1833,7 +1834,8 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
         }
 
         if (proxy->flags & VIRTIO_PCI_FLAG_ATS) {
-            pcie_ats_init(pci_dev, 256);
+            pcie_ats_init(pci_dev, last_pcie_cap_offset);
+            last_pcie_cap_offset += PCI_EXT_CAP_ATS_SIZEOF;
         }
 
         if (proxy->flags & VIRTIO_PCI_FLAG_INIT_FLR) {