tools: add a kernel-chktaint to tools/debugging

Add a script to the tools/ directory that shows if or why the running
kernel was tainted. The script was mostly written by Randy Dunlap; I
enhanced the script a bit.  There does not appear to be a good home for
this script. so create tools/debugging for tools of this nature.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
[ jc: fixed conflicts, rewrote changelog ]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>