PCI: expose function reset capability in sysfs

Some devices allow an individual function to be reset without affecting
other functions in the same device: that's what pci_reset_function does.
For devices that have this support, expose reset attribite in sysfs.

This is useful e.g. for virtualization, where a qemu userspace
process wants to reset the device when the guest is reset,
to emulate machine reboot as closely as possible.

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>