console: make printk() line continuation tracking per-CPU

console: make printk() line continuation tracking per-CPU

This avoids cases where split messages (with other than the initial
part not carrying a log level; single line messages only of course)
issued on multiple CPUs interfere with each other, causing messages to
be issued which are supposed to be suppressed due to the log level
setting. E.g.

	CPU A			CPU B
XENLOG_G_DEBUG "abc"
			XENLOG_G_DEBUG "def\n"
"xyz\n"

would cause the last message to be logged despite this obviously not
being intended (at default log levels).

Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>