powerpc/eeh: Fix fenced PHB caused by eeh_slot_error_detail()
The config space of some PCI devices can't be accessed when their
PEs are in frozen state. Otherwise, fenced PHB might be seen.
Those PEs are identified with flag EEH_PE_CFG_RESTRICTED, meaing
EEH_PE_CFG_BLOCKED is set automatically when the PE is put to
frozen state (EEH_PE_ISOLATED). eeh_slot_error_detail() restores
PCI device BARs with eeh_pe_restore_bars(), which then calls
eeh_ops->restore_config() to reinitialize the PCI device in
(OPAL) firmware. eeh_ops->restore_config() produces PCI config
access that causes fenced PHB. The problem was reported on below
adapter: