[POWERPC] celleb: Add support for PCI Express

This adds support for PCI Express port on Celleb.  I/O space of this
PCI Express port is not mapped in memory space.  So we use the
io-workaround mechanism to make accesses indirect.

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