[PATCH] Fix plist include dependency

plist.h uses container_of, which is defined in kernel.h.
Include kernel.h in plist.h as the kernel.h include does not longer
happen automatically on all architectures.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>