pcib: Add a new IVAR returning the Thunderbolt generation of a bridge

[jhb]

Summary

Use the presence of the new IVAR to determine if a parent pcib device
is a Thunderbolt bridge in tb_pci_probe instead of checking device
IDs.

[obiwac]

looks good, though I wonder if there is a point in actually passing down tb_gen, considering I don't think we'll be supporting non-TB_GEN_USB4 in a while (and I was gonna remove the existing tb_pcib_identifiers after D52861)

[jhb]

I think we just need some sort of IVAR we can test for and this is just as easy as any other. Can you test this to make sure it works? I have only compile tested it as my only FreeBSD box with TB has the older chipsets that don't work.

[obiwac]

In D54158#1237352, @jhb wrote:

I think we just need some sort of IVAR we can test for and this is just as easy as any other. Can you test this to make sure it works? I have only compile tested it as my only FreeBSD box with TB has the older chipsets that don't work.

sorry this is taking a while. I'm looking at this but debugging a panic I'm getting when loading from loader (which for me is required to get the thunderbolt pci bridge to attach - we should probably rename this to something else than tboltX?).

will test as soon as i can