Add NUMA support to powerpc

Add NUMA support to powerpc

Summary:
Initial NUMA support:
    - associate CPU with domain
    - associate memory ranges with domain
    - identify domain for devices
    - limit device interrupt binding to appropriate domain

- Additionally fixes a bug in the setting of Maxmem which led to
  only memory attached to the first socket being enabled for DMA

A pmap variant can opt in to numa support by by calling `numa_mem_regions`
at the end of pmap_bootstrap - registering the corresponding ranges with the
VM.

This yields a ~20% improvement in build times of llvm on dual socket POWER9
over non-NUMA.

Original patch by mmacy.

Differential Revision: https://reviews.freebsd.org/D17933