Any 'bootable' flag in a DOS partition causes boostd to only scan
bootable partitions for that media. This can mean that extlinux.conf
files on the root disk are missed.
Put this logic behind a flag and update the documentation.
For now, the flag is enabled, to preserve existing behaviour. Future
work may provide a command (or some other mechanism) to control this.
Signed-off-by: Simon Glass <sjg@chromium.org>
8c620fd504