Filesystem labeling, paritition sizing, and multiple partition support

I've developed a set of modifications to crochet-freebsd that might be of interest.  They:

1. Allow one to specify sizes and labels for FAT and UFS partitions

2. Allow one to create multiple UFS partitions and run the set of FREEBSD phases on a subset of them.

3. Load geom_label on BeagleBone by default, so labels can be referenced in /etc/fstab

The details of (2) above are in the commit message of 1dbcecd.