This patch implements pci passthrough (hotplug and coldplug) in
libxenlight, it also adds three new commands to xl: pci-attach,
pci-detach and pci-list.
Currently flr on a device is done writing to
/sys/bus/pci/drivers/pciback/do_flr
pciback do_flr is present in both XCI and XCP 2.6.27 kernels.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>