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