powerpc/eeh: Build EEH event based on PE

The original implementation builds EEH event based on EEH device.
We already had dedicated struct to depict PE. It's reasonable to
build EEH event based on PE.

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