In linux_pci_attach_device() allocate a LinuxKPI pci_dev for each device in
the hierarchy up to the root port[1] as we cannot do that later on demand
as we may be in a context where we may not sleep.

Take special care of DRM as there is a non-PCI device in the chain which
needs to be skipped.

iwlwifi(4) can hit this case called from a callout.

While here leave a comment sa the cleanup order of
linux_pci_attach_device() needs correction seperately.

Sponsored by: The FreeBSD Foundation
PR: 283027
Suggested by: jhb [1]
MFC after: 3 days