pkgbase: Put geom utilities in their own package

For most users it's not needed to boot and they are also
available in the FreeBSD-rescue package in case an update
break and FreeBSD-geom package isn't updated correctly.

Differential Revision: https://reviews.freebsd.org/D36224

(cherry picked from commit 0bf688786f7d5508b43b50c62f50f022e33b1352)