Various chromebooks: depthcharge images are too big

Right now a lot of chromebook related images fail to build in bpo:

Building depthcharge image for board 'HP Chromebook 14 G3' ('blaze').
Image with compression 'none' is too big for this board.
Couldn't build a small enough image for this board. This is usually solvable by making the initramfs smaller, check your OS's documentation on how to do so.

I guess this is due to new options being enabled in the kernels. Looks like depthcharge compression is now possible, can we use something other than 'none' and see if that fixes it?

It should be possible to reproduce this locally, just try to build an image for one of these devices.

CC: @craftyguy, @calebccff, @jenneron, @adamthiede, @JustSoup321, @alpernebbi (people also tagged in #2914 (closed))