can: slcan/vcan: eliminate banner[] variable, switch to pr_info()

Several can modules in drivers/net/can use a banner[] variable at the
top which defines a string that is used once during init.  This string
is also embedded with KERN_INFO which makes it printk() specific.

Improve the code by eliminating the banner[] variable and moving the
string to where it is printed.  Then switch from printk(KERN_INFO to
pr_info() for the lines that were changed.

This patch is similar to [1] which was applied to net/can.

  [1]: https://lkml.org/lkml/2014/11/22/10



Signed-off-by: Jeremiah Mahler <jmmahler@gmail.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>