powerpc/eeh: Search PE based on requirement

The patch implements searching PE based on the following
requirements:

 * Search PE according to PE address, which is traditional
   PE address that is composed of PCI bus/device/function
   number, or unified PE address assigned by firmware or
   platform.
 * Search parent PE according to the given EEH device. It's
   useful when creating new PE and put it into right position.

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