LSM: Add security_path_chroot().

This patch allows pathname based LSM modules to check chroot() operations.

This hook is used by TOMOYO.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>
(cherry picked from commit 8b8efb44

)

Signed-off-by: Andy Whitcroft <apw@canonical.com>