Add a sysfs attribute to query the type of the touchscreen device.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Link: https://lore.kernel.org/r/20210125182527.1225245-5-l.stach@pengutronix.deSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>