[U-Boot] Kconfiglib documentation generation

[Ulf Magnusson]

Hello,

Just as an FYI, Kconfiglib 2 (https://github.com/ulfalizer/kconfiglib)
can generate nice Kconfig docs. See
http://docs.zephyrproject.org/reference/kconfig/index.html for example
output (warning: heavy page, lots of symbols).

The script that generates the RST output for those docs is at
https://github.com/zephyrproject-rtos/zephyr/blob/master/doc/scripts/genrest.py.
It deals well with symbols defined in multiple locations as well
(plenty of those in Zephyr too), listing each definition with the
correct properties.

I just added a patch to Kconfiglib that reduces the parsing time for
the U-Boot Kconfigs from about four seconds to about half a second as
well (Core i7 2600k). Those symbols defined in a million locations
triggered some redundant work earlier. :)

Cheers,
Ulf