ieee1394: eth1394: bring back a parent device

This adds a real parent device to eth1394's ethX device like in Linux
2.6.20 and older.  However, due to unfinished conversion of the ieee1394
away from class_device, we now refer to the FireWire controller's PCI
device as the parent, not to the ieee1394 driver's fw-host device.

Having a real parent device instead of a virtual one allows udev scripts
to distinguish eth1394 interfaces from networking bridges, bondings and
the likes.

Fixes a regression since 2.6.21:
https://bugs.gentoo.org/show_bug.cgi?id=177199

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>