[POWERPC] Use ARRAY_SIZE macro when appropriate

Use ARRAY_SIZE macro already defined in linux/kernel.h

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>