• Remove 'struct vmmeter' from 'struct pcpu', leaving only global vmmeter in place. To do per-cpu stats, convert all fields that previously were maintained in the vmmeters that sit in pcpus to counter(9).
• Since some vmmeter stats may be touched at very early stages of boot, before we have set up UMA and we can do counter_u64_alloc(), provide an early counter mechanism: o Leave one spare uint64_t in struct pcpu, named pc_early_dummy_counter. o Point counter(9) fields of vmmeter to pcpu[0].pc_early_dummy_counter, so that at early stages of boot, before counters are allocated we already point to a counter that can be safely written to. o For sparc64 that required a whole dummy pcpu[MAXCPU] array.

Further related changes:

• Don't include vmmeter.h into pcpu.h.
• vm.stats.vm.v_swappgsout and vm.stats.vm.v_swappgsin changed to 64-bit, to match kernel representation.
• struct vmmeter hidden under _KERNEL, and only vmstat(1) is an exclusion.

This is based on benno@'s 4-year old patch:
https://lists.freebsd.org/pipermail/freebsd-arch/2013-July/014471.html

Reviewed by: kib, gallatin, marius, lidl
Differential Revision: https://reviews.freebsd.org/D10156