Document the dispatch path added by the former commit
fs: dispatch null_dev_desc_ok filesystems before lookup
Add a null-block-device interfaces section that:
* lists the three fstypes that can benefit of it (semihosting, ubifs,
sandbox) and the CONFIG option that builds each
* explains the '-' convention for the unused <dev[:part]> field
Suggested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Vincent Jardin <vjardin@free.fr>
Reviewed-by: Simon Glass <sjg@chromium.org>