The bdinfo command makes use of quite a few functions which show a label
followed by a value, on a single line.
This sort of thing is generally useful outside of bdinfo, so move it to
a generic place. Use 'l' (for label) as the prefix.
The margin is still hard-coded to 12, which seems a reasonable limit for
a label.
Signed-off-by: Simon Glass <sjg@chromium.org>