[POWERPC] Celleb: Support PCI bus and base of I/O

This patch includes support for pci buses, base of Celleb specific
devices, and etc. It works on of_platform bus.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>