powerpc/powernv: Using PCI core to do resource assignment

Currently, the PCI probe flags "PCI_PROBE_ONLY | PCI_REASSIGN_ALL_RSRC"
used on powernv platform. That means the platform has to do the PCI
resource assignment by itself.

The patch changes the PCI probe flag to "PCI_REASSIGN_ALL_RSRC" so
that the PCI core will do the resource assignment. Also, the I/O
and MMIO minimal alignment for P2P bridges have been configured
while doing fixup for the PHBs.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Reviewed-by: Ram Pai <linuxram@us.ibm.com>
Reviewed-by: Richard Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>