[POWERPC] Add a field for each specific bus to struct pci_controller

Struct pci_controller doesn't prepare for the dependent data of each
specific bus. This patch adds private member to struct pci_controller.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>