[POWERPC] pSeries: EEH improperly enabled for some Power4 systems

It appears that EEH is improperly enabled for some Power4 systems.
On these systems, the ibm,set-eeh-option returns a value of success
even when EEH is not supported on the given node. Thus, an explicit
check for support is required.

During boot, on power4, without this patch, one sees messages
similar to:

EEH: event on unsupported device, rc=0 dn=/pci@400000000110/IBM,sp@1
EEH: event on unsupported device, rc=0 dn=/pci@400000000110/pci@2
EEH: event on unsupported device, rc=0 dn=/pci@400000000110/pci@2,2
etc.

The patch makes these go away.

Without this patch, EEH recovery does seem to work correctly for
at least some devices (I tested ethernet e1000), but fails to
recover others (the Emulex LightPulse LPFC, most notably).
Off the top of my head, I don't remember why some devices are
affected, but not others.

The PAPR indicates that the correct way to test for EEH is as
done in this patch; its not clear to me if this was in the PAPR
all along, or recently added; if it was there all along, its not
clear to me why this hadn't been fixed long ago. I suspect only
certain firmware levels are affected.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>