7970 zfs_arc_num_sublists_per_state should be common to all multilists

illumos/illumos-gate@10fbdecb05f411234920f8d3c92c148d39106d7e
https://github.com/illumos/illumos-gate/commit/10fbdecb05f411234920f8d3c92c148d39106d7e

https://www.illumos.org/issues/7970

The global tunable zfs_arc_num_sublists_per_state is used by the ARC and
the dbuf cache, and other users are planned. We should change this
tunable to be common to all multilists.

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Matthew Ahrens <mahrens@delphix.com>