EEH + hotplug fixes

[Oliver O'Halloran]

Fixes various random crashes and other bad behaviour when hot
pluggable slots are used with EEH, namely:

1) Random crashes due to eeh_pe and pci_dn lifecycle mis-management
2) Hotplug slots tearing down devices you are trying to recover due
   to the reset that occurs while recovering a PE / bus.
3) Hot-remove causing spurious EEH events.

And some others. This series also enables pnv_php on Power9
since various people were carrying around hacks to make it
work and with the above fixes it seems to be fairly stable
now.

The series also adds the beginnings of a platform-independent test
infrastructure for EEH and a selftest script that exercises the
basic recovery path.

Oliver