Revert "writeback: remove nr_pages_dirtied arg from balance_dirty_pages_ratelimited_nr()"

This reverts commit a58846bffd339a3d8c6a5efa308195eaa59289c1.
Revert "CPU hotplug, writeback: Don't call writeback_set_ratelimit() too often during hotplug"

This reverts commit 66163972806060a2a42a74ceefdeb09f033e509e.