pkgbase: Put zfs utilities and lib in their own package

It is useful to have zfs utilities and lib in a separate package as
it allow users to create image that can support ZFS (i.e. not with
WITHOUT_ZFS in src.conf set) without bloating the default image with
all zfs tools (for example for jails).

Differential Revision: https://reviews.freebsd.org/D36225

(cherry picked from commit a71ea7bea0d2a8ba86373377c3c1443acbeab5d2)