[POWERPC] spu_base: remove cleanup_spu_base

spu_base.c is always built into the kernel image, so there is no need
for a cleanup function.  And some of the things it does are in the
way for my following patches, so I'd rather get rid of it ASAP.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>