include/linux/printk.h: add pr_<level>_once macros

- Move printk_once definitions and add an #ifdef CONFIG_PRINTK

- Add pr_<level>_once so printks can use pr_fmt

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>