[POWERPC] Celleb: setup sio in SCC

This patch setup serial interfaces in SCC to work with serial_txx9
driver.

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>