Start implementing queue state updates using fcmpset loops. [3/5]

[markj]

Summary

The active queue scan updates act_count based on the return value of
pmap_ts_referenced() and whether PGA_REFERENCED is set. It deactivates
the page if the activation count goes to zero. Implement this logic
using vm_page_pqstate_commit().

[markj]

Rename the next_page target to skip_page, and unbusy the page at the end
of the loop instead of having lots of inline calls to vm_page_xunbusy().

[jeff]

Looks like the wrong comment for this patch? That is describing inactive or laundry.

[markj]

Committed in r356155.