powerpc/eeh: Replace pci_dn with eeh_dev for EEH on pSeries

The pci_dn has been replaced with eeh_dev. In order to comply with
the rule, the EEH platform implementation on pSeries should also
be adjusted for a little bit so that it will depend on eeh_dev instead
of pci_dn.

The patch replaces pci_dn with eeh_dev. The corresponding information
will be retrieved from eeh_dev instead of pci_dn.

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