powerpc/powernv: Fetch frozen PE on top level

It should have been part of commit 1ad7a72c

 ("powerpc/eeh: Report
frozen parent PE prior to child PE"). There are 2 ways to report
EEH errors: proactively polling because of 0xFF's returned from
PCI config or IO read, or interrupt driven event. We missed to
report and handle parent frozen PE prior to child frozen PE for
the later case on PowerNV platform.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>