Devicetree support in about-distro

Hi,

This is a preliminary attempt at adding support for Open Firmware/DT systems.

A lot of non-x86 consumer systems, particularly SBCs and other embedded devices, forego the traditional SMBIOS/DMI interface for Devicetree. A lot of the information that can be retrieved from the FDT is functionally similar to what you get on a PC over DMI (serial numbers, firmware versions, et cetera) and it is useful for users to have easy access to this. This is especially so as these sorts of devices are now trickling up into the traditional desktop space.

One problem regarding the portability of this feature set is that there is no standard way to access the Devicetree across OSes. I have added Linux support because it is simple and probably the most immediately beneficial. The BSDs, however, do not expose the FDT as a filesystem and require the use of a binary utility to read data out of it, similar to how DMI is handled now. I have marked this as a draft for this reason, as I'm not quite sure how this should be handled long term.

James