alsa-state: correct license

* add GPL license because of alsa-state-init file
* gpl link points to gpl3, but at time of adding this file was actually
  pointing to gpl2, so should correspond to SPDX GPL-2.0-or-later
* remove date as the file was already changed several times since then

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>