numa, cpumask: move numa_node_id default implementation to topology.h, fix

Impact: build fix for powerpc and sparc

Today's linux-next build (powerpc allyesconfig) failed like this:

> In file included from include/linux/mmzone.h:776,
>                  from include/linux/gfp.h:5,
>                  from include/linux/kmod.h:23,
>                  from include/linux/module.h:14,
>                  from init/version.c:11:
> arch/powerpc/include/asm/mmzone.h:32: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'numa_cpumask_lookup_table'

Caused by commit 082edb7b

 ("numa,
cpumask: move numa_node_id default implementation to topology.h") from
the cpus4096 tree which removed the include of linux/topology.h from
linux/mmzone.h.

Same for sparc64 defconfig.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-b: Rusty Russell <rusty@rustcorp.com.au>
Cc: ppc-dev <linuxppc-dev@ozlabs.org>
LKML-Reference: <20090319220322.3baa4613.sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>