Add GELI partition types

[eric_metricspace.net]

Summary

This adds a freebsd-geli partition type to the necessary tables. This allows users to mark their GELI partitions without revealing the underlying contents, avoiding an information leak to a potential attacker (however minor).

Test Plan

Need to test:

• Userland gpart tool
• Kernel detection

[eric_metricspace.net]

Turns out this one is nowhere near complete. Need to add more stuff.

However, this one also isn't *strictly* necessary for GELI.

[eric_metricspace.net]

This review actually needs more work. Turns out there's more places where things need to be added.