Input: atmel_mxt_ts - remove platform data support

Now that there are no users of custom Atmel platform data, and everyone
has switched to the generic device properties, we can remove support for
the platform data.

Acked-by: Nick Dyer <nick@shmanahar.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Benson Leung <bleung@chromium.org>