Input: usbtouchscreen - add support for ET&T TC4UM touchscreen controller

This patch adds support for the ET&T TC4UM 4-wire USB touchscreen
controller and tries to reuse the bits for TC5UH controller in kernel
already. Data interface is same.

Tested-by: Roger Pueyo Centelles <rogerpueyo@rogerpueyo.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>