test flashing HEADS (internally) / make the transition easy

[merge]

We want to make it easy to quickly "bootstrap" the X230 to a working, unlocked, easy to use coreboot-based flash image system; SeaBIOS is great for this!

There surely are users that want to move on to HEADS from there, especially when some of purism's work is merged. I'd love to have this tested (and documented maybe).

• figure out what branch of HEADS with or without what changes to build
• build the x230 HEADS image from today's master (?) branch
• how do the flash regions look? They use 7M for the BIOS? Test flashing internally.
• Test flashing back to our latest image.
• write a script for flashing a (full) heads image, similar to x230_update.sh

[merge]

• The master branch seems ok. There doesn't seem to be much outside of it. That's great!
• They use 7M CBFS size, so the bios layout start at 00500000, not 00800000. Their initrd has all the flashrom setup we want to test from an external system.

[merge]

just some notes and loud thinking:

needed for building (Linux in general, in part) on Debian:
zlib1g-dev uuid-dev libdigest-sha-perl bc bzip2 bison flex git gnupg iasl m4 nasm patch python wget libssl-dev libelf-dev

after cloning:

make to build toolchains (probably isn't necessary)
build/make-4.2/make BOARD=x230

[merge]

tested, script added. done.