All guest devices now use a common device address structure
summarized by:

  enum virDomainDeviceAddressType {
    VIR_DOMAIN_DEVICE_ADDRESS_TYPE_NONE,
    VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI,
  };

  struct _virDomainDevicePCIAddress {
    unsigned int domain;
    unsigned int bus;
    unsigned int slot;
    unsigned int function;
  };

  struct _virDomainDeviceInfo {
    int type;
    union {
        virDomainDevicePCIAddress pci;
    } addr;
  };

This replaces the anonymous structs in Disk/Net/Hostdev data
structures. Where available, the address is *always* printed
in the XML file, instead of being hidden in the internal state
file.

  <address type='pci' domain='0x0000' bus='0x1e' slot='0x07' function='0x0'/>

The structure definition is based on Wolfgang Mauerer's disk
controller patch series.

* docs/schemas/domain.rng: Define the <address> syntax and
  associate it with disk/net/hostdev devices
* src/conf/domain_conf.h, src/conf/domain_conf.c,
  src/libvirt_private.syms: APIs for parsing/formatting address
  information. Also remove the QEMU specific 'pci_addr' attributes
* src/qemu/qemu_driver.c: Replace use of 'pci_addr' attrs with
  new standardized format.