Input: libps2 - attach ps2dev instances as serio port's drvdata

In preparation of having unified interrupt handler for PS/2 devices,
instead of attaching instances of psmouse and atkbd structures as serio's
driver data, switch to attaching ps2dev instances.

Reviewed-by: Raul Rangel <rrangel@chromium.org>
Link: https://lore.kernel.org/r/20230511185252.386941-2-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>