printk: add con_printk() macro for console details

It is useful to generate log messages that include details about
the related console. Rather than duplicate the code to assemble
the details, put that code into a macro con_printk().

Once console printers become threaded, this macro will find more
users.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-9-john.ogness@linutronix.de