Add more lowmem predicates.

[markj]

Summary

Use these predicates instead of inline references to vm_min_domains.
Also add an all_domains set, akin to all_cpus; this can be used to check
whether all domains are below a threshold, e.g.,
vm_page_count_min(&all_domains).

[kib]

sys/x86/acpica/srat.c

475

Wouldn't this initialize all_domains only on x86 ?

[markj]

• Add a static initializer for all_domains.

[jeff]