bootstd: Record the bootdevs used during scanning

Add a way to record the bootdevs used when scanning for bootflows. This is
useful for testing.

Enable this only with BOOTSTD_FULL and do the same for the progress
reporting.

Re-enable and update the affected tests now that we have this feature.

For bootdev_test_order_default() there is no-longer any support for using
the bootdev aliases to specify an ordering, so drop that part of the test.

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