Input: atmel_mxt_ts - add support for reset line

Provide support for controlling reset pin. If this is not driven
correctly the device will be held in reset and will not respond.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>