build_image: Add building minios initramfs kernel

And writing the kernel into the MINIOS-A partition of the disk
image. This allows us to move forward with the rest of the minios
implementation including signing, paygen, updates, etc.

BUG=b:187177283
TEST=./build_image --board zork-minios test

Cq-Depend: chromium:2872568
Change-Id: I9fac016f8e43160a49961b5209650ffd565e2996
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2872586
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
1 file changed