This patch adds mock of the /dev/vfio path, needed for proper
implementation of the support for multifunction/multiple devices
per iommu groups.

To do that, the existing bind and unbind operations were adapted
to operate with the mocked filesystem as well.
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>