Remap keyboard to use in-firmware dvorak layout.

Normally I keep my dvorak mapping in the OS so that I can plug in an
external keyboard and use the same mapping across both, but with the
Reform the built-in keyboard is good enough that it doesn't make me
want to use an external one. (but it still could be better!)

This layout is roughly Atreus inspired in that it puts ctrl and alt on
the middle two thumb keys, but the keyboard border cover makes those
two keys oddly difficult to hit using your thumb, so I end up using
the more conventionally-located ctrl and alt keys instead.

Future revision would add an fn key and a numpad on the fn layer, but
let's take this one step at a time.