PCI/IOV: Introduce pci_iov_sysfs_link() function

PCI/IOV: Introduce pci_iov_sysfs_link() function

Currently pci_iov_add_virtfn() scans the SR-IOV BARs, adds the VF to the
bus and also creates the sysfs links between the newly added VF and its
parent PF.

With pdev->no_vf_scan fencing off the entire pci_iov_add_virtfn() call
s390 as the sole pdev->no_vf_scan user thus ends up missing these sysfs
links which are required for example by QEMU/libvirt.

Instead of duplicating the code refactor pci_iov_add_virtfn() to make
sysfs link creation callable separately.

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Link: https://lore.kernel.org/r/20200506154139.90609-1-schnelle@linux.ibm.com
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>