tablet: add a the Totem tool type to the tablet interface

This is the public API only, not the internal bits, so nothing will work just
yet.

This interface addition is for the Dell Canvas Totem tool, so let's go with
the same name because options like "Rotary" are too ambiguous.

The totem is a knob that can be placed on the surface, it provides us with
location and rotation data. The touch major/minor fields are filled in by the
current totem, but they're always the same size.

The totem exports BTN_0 as well, so let's add that to the debug-events output.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>