If we set squashfs rootfsType, the image doesn't rebuild when the kernel config is changed. Need to figure out why
It will probably work fine for USB-stick boot (except in the case where there is > 1 usb device plugged in, so maybe don't do that) It doesn't matter for TFTP boot because boot.scr overrides the root= param anyway
it adds ~ 5MB to the image size
ideally we would make this a module instead of compiling in directly
