sysmouse(4): Add wsp(4)-style T-Axis reporting.

Neither the ums(4) nor psm(4) reporting can be used by the wsp(4)
driver, as they rely on static-length movements, while wsp(4) may need
to scroll in large amounts per evdev event push.

This style uses a false button-5 press as an indicator that the z-axis
movement is a horizontal scroll, otherwise a vertical scroll.

Signed-off-by: Joshua Rogers <Joshua@Joshua.Hu>