powerpc/pci: Trace more information from pci_dn

Originally, EEH probes on device_node or pci_dev and populates the
corresponding eeh_dev. In the subsequent patches, EEH will probes
on pci_dn and populates the corresponding eeh_dev. So we have to
cache some information in pci_dn, either from device_node or SRIOV
PF's enablement platform hook, to populate the eeh_dev properly.

The motivation to probe pci_dn, instead of device node or pci_dev,
to populate eeh_dev is SRIOV VFs are dynamically created and we
don't have the corresponding device nodes for them.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>