powerpc/eeh: Create PEs duing EEH initialization

The patch creates PEs and associated the newly created PEs with
it parent/silbing as well as EEH devices. It would become more
straight to trace EEH errors and recover them accordingly.

Once the EEH functionality on one PCI IOA has been enabled, we
tries to create PE against it. If there's existing PE, to which
the current PCI IOA should be attached, the existing PE will be
converted from "device" type to "bus" type accordingly.

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