It wasn't hugely clear what the platform ID was actually meant to represent. In
some cases it was being used like a physical ID, in others it was a logical ID,
and in others it was both. In some cases it was even used as a sysfs path.
Clear up all the confusion by splitting the platform ID into two parts, an
optional *physical* ID to represent the electrical connection, and an optional
*logical* ID to disambiguate composite devices with the same physical ID.
Also create an explicit sysfs_path getter for FuUdevDevice to make this clear.
This allows WAIT_FOR_REPLUG to always work, rather than depending on the order
that the GUIDs were added, and that the kernel would always return the same
sysfs path (which it doesn't have to do, especially for hidraw devices).
