Export per-domain cpusets to userland.

[jhb]

Summary

Create a cpuset mask for each NUMA domain that is available in the
kernel via the global cpuset_domain[] array. To export these to userland,
add a CPU_WHICH_DOMAIN level that can be used to fetch the mask for a
specific domain. Add a -d flag to cpuset(1) that can be used to fetch
the mask for a given domain.

Submitted by: jeff (kernel bits)

Test Plan

Verify that 'cpuset -gd <n>' works for both domains on a Westmere box.

[adrian]

Superficially - looks good to me.