touch_TouchscreenScroll uses four gesture files per device.

<DEVICE_NAME>_touchscreen_Touch ID_scroll-* for [up, down, left, right]

Single finger is pressed to touchscreen and then dragged in the direction
indicated.  Make no stray marks with additional fingers and do not pause the
scroll during the movement.  Scroll should be continuous.

Name refers to the physical direction the finger is moving.  E.g.
samus_touchscreen_scroll-up refers to a single finger moving from the
side of the screen closest to hinges up to the oposite side of the screen.