[POWERPC] Celleb: setup usb host controller in SCC

USB host controller in SCC requires enable sequence. It should be done
before USB host drivers start.

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>