xHCI host controller may register two (or more?) USB root hubs for USB
2.0 and USB 3.0, and devices under the hubs may have same ID_PATH.
So, to avoid the conflict, let's introduce ID_PATH_WITH_USB_REVISION
that includes the USB revision.
Closes#19406.
Add the i2c subsystem to those that create by-path links.
i2c devices may not have IDs so we can't rely on the by-id links
but they (or some of them) should at least have a path that we can use.
This change is only about the source tree. We have tmpfiles.d/, modprobe.d/,
sysctl.d/, and sysusers.d/, but for historical reasons, rules/ didn't fit this
pattern. We also *install* it as rules.d/. Let's rename to be consistent.
