When bootloader spec is used to boot devices it is often desirable
to boot the same image from different media. Since the fs images
need to contain the root= parameters to tell Linux where to boot
from the images can't be identical on different media.
This patch changes this by introducing a 'appendroot' option for
bootloader spec. If set to true, barebox will construct a Linux
commandline option for the device the bootloader spec entry is found
on.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>