console: move for_each_console to linux/console.h

Move it out of printk.c so that we can use it all over the code. There
are some potential users which will be converted to that macro in next
patches.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>