powerpc/eeh: Make EEH device add/remove more robust

To properly fix PCI hotplug, it's useful to be able to make the fixup
passes on all devices whether they were just hot plugged or already
there.

The EEH code however used to not be very friendly with calling
eeh_add_device_late() multiple time, and not very rebust in the way it
generally tests whether a device is in the expected state vs. the EEH
code.

This improves it, along with cleaning up a couple of debug printk's.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>