tty: fix up a few remaining files without SPDX identifiers

There were a few straggling files under drivers/tty/ that did not have
any SPDX identifier either because they entered the tree recently, or
they somehow missed the mass-tagging of commit b2441318 ("License
cleanup: add SPDX GPL-2.0 license identifier to files with no license")

This commit follows the same rule as b2441318

 ("License cleanup: add
SPDX GPL-2.0 license identifier to files with no license") where files
without any specified license in them fall under GPL-2.0 as the correct
license for the individual file.  Add that identifier to these remaining
files so that we don't have to guess at the license of them in the
future.

Cc: Jiri Slaby <jslaby@suse.com>
Cc: "David S. Miller" <davem@davemloft.net>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>