powerpc/eeh: Replace pci_dn with eeh_dev for EEH address cache

With original EEH implementation, struct pci_dn is used while building
PCI I/O address cache, which helps on searching the corresponding
PCI device according to the given physical I/O address. Besides, pci_dn
is associated with the corresponding PCI device while building its
I/O cache.

The patch replaces struct pci_dn with struct eeh_dev so that EEH address
cache won't depend on struct pci_dn. That will help EEH to become an
independent module in future. Besides, the binding of eeh_dev and PCI
device is done while building PCI device I/O cache.

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