Add files for r327895

Implement 'domainset', a cpuset based NUMA policy mechanism. This allows
userspace to control NUMA policy administratively and programmatically.

Implement domainset based iterators in the page layer.

Remove the now legacy numa_* syscalls.

Cleanup some header polution created by having seq.h in proc.h.

Reviewed by: markj, kib
Discussed with: alc
Tested by: pho
Sponsored by: Netflix, Dell/EMC Isilon
Differential Revision: https://reviews.freebsd.org/D13403