powerpc/pci: Remove VFs prior to PF

As commit ac205b7b ("PCI: make sriov work with hotplug remove")
indicates, VFs which is on the same PCI bus as their PF, should be
removed before the PF. Otherwise, we might run into kernel crash
at PCI unplugging time.

This applies the above pattern to powerpc PCI hotplug path.

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