"volatile considered harmful"

Encourage developers to avoid the volatile type class in kernel code.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>