udev: Use parent bus id for virtio disk builtin path-id (#5500)

udev: Use parent bus id for virtio disk builtin path-id (#5500)

The builtin path id for virtio block devices has been changed
to use the bus id without a prefix "virtio-pci" to be
compatible with all virtio transport types.

In order to not break existing setups, the by-path symlinks for
virtio block devices on the PCI bus are reintroduced by udev rules.
The virtio-pci symlinks are considered to be deprecated and
should be replaced by the native PCI symlinks.

Example output for a virtio disk in PCI slot 7:
 $ ls  /dev/disk/by-path
 pci-0000:00:07.0
 pci-0000:00:07.0-part1
 virtio-pci-0000:00:07.0
 virtio-pci-0000:00:07.0-part1

See also
[1] https://lists.freedesktop.org/archives/systemd-devel/2017-February/038326.html
[2] https://lists.freedesktop.org/archives/systemd-devel/2017-March/038397.html

This reverts f073b1b but keeps the same symlinks for compatibility.