pcie: helper functions for pcie capability and extended capability

This patch implements helper functions for pci express capability
and pci express extended capability allocation.
NOTE: presence detection depends on pci_qdev_init() change.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci.h

@@ -9,6 +9,8 @@
 /* PCI includes legacy ISA access.  */
 #include "isa.h"
 
+#include "pcie.h"
+
 /* PCI bus */
 
 #define PCI_DEVFN(slot, func)   ((((slot) & 0x1f) << 3) | ((func) & 0x07))
@@ -175,6 +177,9 @@ struct PCIDevice {
     /* Offset of MSI capability in config space */
     uint8_t msi_cap;
 
+    /* PCI Express */
+    PCIExpressDevice exp;
+
     /* Location of option rom */
     char *romfile;
     ram_addr_t rom_offset;