[POWERPC] Fix CONFIG_SMP=n build break

Fix two build errors on powerpc allyesconfig + CONFIG_SMP=n:

arch/powerpc/platforms/built-in.o: In function `cpu_affinity_set':
arch/powerpc/platforms/cell/spu_priv1_mmio.c:78: undefined reference to `.iic_get_target_id'
arch/powerpc/platforms/built-in.o: In function `iic_init_IRQ':
arch/powerpc/platforms/cell/interrupt.c:397: undefined reference to `.iic_setup_cpu'

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>