exynos 5 chromebooks: booting from USB does not work

We need one simple thing to support it: kernel modules for USB on initramfs stage.

There is also a problem that exynos 5 chromebooks are very picky about USB sticks, it is hit and miss. I haven't found any suitable USB stick at my home, so I can't test these changes. We also don't have anyone from Testing Team (wiki) with these devices. So the blocker for this issue is not being able to test related changes.

Meanwhile, these devices can be booted from a SD card