powerpc/eeh: Output PHB diag-data

When hitting frozen PE or fenced PHB, it's always indicative to
have dumped PHB diag-data for further analysis and diagnosis.
However, we never dump that for the cases. The patch intends to
dump PHB diag-data at the backend of eeh_ops::get_log() for PowerNV
platform.

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