This adds two features that can be set in the rootfs that Qi is checking.
- if it finds /boot/noboot-<device>, eg /boot/noboot-GTA02 then it will
skip the rootfs for booting and try the next one if any
- if it finds /boot/append-<device>, eg, /boot/append-GTA02 then it will
append the contents of this file to the kernel commandline.
Signed-off-by: Andy Green <andy@openmoko.com>