Implement several enhancements to NUMA policies.

Add a new "interleave" allocation policy which stripes pages across
domains with a stride or width keeping contiguity within a multi-page
region.

Move the kernel to the dedicated numbered cpuset #2 making it possible
to assign kernel threads and memory policy separately from user. This
also eliminates the need for the complicated interrupt binding code.

Add a sysctl API for viewing and manipulating domainsets. Refactor some
of the cpuset_t manipulation code using the generic bitset type so that
it can be used for both. This probably belongs in a dedicated subr file.

Attempt to improve the include situation.

Reviewed by: kib
Discussed with: jhb (cpuset parts)
Tested by: pho (before review feedback)
Sponsored by: Netflix, Dell/EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14839