printk: add KERN_CONT annotation

printk: add the KERN_CONT annotation (which is empty string but via
which checkpatch.pl can notice that the lacking KERN_ level is fine).
This useful for multiple calls of hand-crafted printk output done by
early debug code or similar.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>