[POWERPC] Added self_busno to indicate which bus number the PHB is

Added self_busno to pci_controller and indirect PCI ops to be set by
board code to indicate which bus number to use when talking to the PHB.
By default we use zero since the majority of controllers that have
implicit mechanisms to talk to the PHBs use a bus number of zero.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>