The function pci_devs_phb_init is invoked more earlier than we really
probe the pci controller, so it does nothing at all. And we also don't
need the pci_dn stuff for the fsl powerpc64 boards, just remove it.

It also seems that we don't support ISA on all the current corenet ds
boards. So picking a primary bus seems useless, remove that function
too.
Signed-off-by: Kevin Hao <haokexin@gmail.com>