[POWERPC] celleb: Add support for native CBE

This adds support for native CBE on Celleb, that is, without the BEAT
hypervisor.  Many codes in platforms/cell/ are used in native CBE
environment.

Signed-off-by: Kou Ishizaki <Kou.Ishizaki@toshiba.co.jp>
Signed-off-by: Paul Mackerras <paulus@samba.org>