powerpc/eeh: Fix missed PE#0 on P7IOC

PE#0 should be regarded as valid for P7IOC, while it's invalid for
PHB3. The patch adds flag EEH_VALID_PE_ZERO to differentiate those
two cases. Without the patch, we possibly see frozen PE#0 state is
cleared without EEH recovery taken on P7IOC as following kernel logs
indicate:

[root@ltcfbl8eb ~]# dmesg
       :
pci 0000:00     : [PE# 000] Secondary bus 0 associated with PE#0
pci 0000:01     : [PE# 001] Secondary bus 1 associated with PE#1
pci 0001:00     : [PE# 000] Secondary bus 0 associated with PE#0
pci 0001:01     : [PE# 001] Secondary bus 1 associated with PE#1
pci 0002:00     : [PE# 000] Secondary bus 0 associated with PE#0
pci 0002:01     : [PE# 001] Secondary bus 1 associated with PE#1
pci 0003:00     : [PE# 000] Secondary bus 0 associated with PE#0
pci 0003:01     : [PE# 001] Secondary bus 1 associated with PE#1
pci 0003:20     : [PE# 002] Secondary bus 32..63 associated with PE#2
       :
EEH: Clear non-existing PHB#3-PE#0
EEH: PHB location: U78AE.001.WZS00M9-P1-002

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