virpcimock: Mock the SRIOV Virtual functions

virpcimock: Mock the SRIOV Virtual functions

The softlink to physfn is the way to know if the device is
VF or not. So, the patch softlinks 'physfn' to the parent function.
The multifunction PCI devices dont have 'physfn' softlinks.

The patch adds few Virtual functions to the mock environment and
changes the existing VFIO test xmls using the VFs to use the newly
added VFs for their use case.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>