PCI passthrough merge completion

PCI passthrough merge completion

Remaining parts of xen-unstable c/s
15891:acfa9290746f9c00e30dca7a62e9f7a96702b3b5:

    PCI passthru: tools changes (generic and vt-d)

    I have added CONFIG_PASSTHROUGH in ioemu/Makefile.target and
    ioemu/hw/pc.c in attached vtd_tools2.patch.  This should turn off
    libpci usage by default until user specifically enables it.

    This can be safely check-in without breaking builds for people who do
    not care about pass-through devices.  I will try to think of a better
    way to enable this.

    Signed-off-by: Allen Kay <allen.m.kay@intel.com>
    Signed-off-by: Guy Zana <guy@neocleus.com>