We need extensions to be set up before we start trying to boot any of the
bootdevs. Add a new priority before all the others for tht sort of thing.
Also add a 'none' option, so that the first one is not 0.
While we are here, comment enum bootdev_prio_t fully and expand the test
for the 'bootdev hunt' command.
Signed-off-by: Simon Glass <sjg@chromium.org>
Add a bootdev for SPI flash so that these devices can be used with
standard boot. It only supports loading a script.
Add a special case for the label, since we want to use "spi", not
"spi_flash".
Enable the new bootdev on sandbox.
Signed-off-by: Simon Glass <sjg@chromium.org>
