It seems better to call this a 'bootdev' since this is name used in the
documentation. The older 'Bootdevice' name is no-longer used and may cause
confusion with the 'bootdevice' environment variable.

Update throughout to use bootdev.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

This causes crashes on some boards, e.g. rockpro64. In any case, we
should not do it.

Check the usb_started flag to avoid this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Tested-by: Tom Rini <trini@konsulko.com>

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 hunter for USB which enumerates the bus to find new bootdevs.

Update the tests and speed up bootdev_test_prio() while we are here, by
dropping the USB delays.

Signed-off-by: Simon Glass <sjg@chromium.org>

The code in these functions turns out to often be the same. Add a default
get_bootflow() function and allow the drivers to select it by setting
the method to NULL.

This saves a little code space.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a bootdev driver for USB host. It can use the distro boot mechanism to
locate a file, or any other available bootmeth.

Signed-off-by: Simon Glass <sjg@chromium.org>