powerpc/powernv: Group VF PE when IOV BAR is big on PHB3

When IOV BAR is big, each is covered by 4 M64 windows.  This leads to
several VF PE sits in one PE in terms of M64.

Group VF PEs according to the M64 allocation.

[bhelgaas: use dev_printk() when possible]
Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>