[POWERPC] cell: Fix spufs with "new style" device-tree

Some SPU code was a bit too convoluted and broke when adding support for
the new style device-tree, most notably the struct pages for SPEs no
longer get created. oops...

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>