Fix <linux/log2.h> kernel-doc:
- Add kernel-doc notation to some functions.
- Fix kernel-doc notation in function parameters.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
[andrew.smirnov@gmail.com: Applied kernel patch to Barebox as-is]
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>