These devices have a pen device and a touch device through the same serial
protocol, split it up into two separate devices like we do for USB Wacom
tablets too.

Userspace already matches on the device name so we can't drop it
completely. Compose the same basename based on capabilities and append the
tool type, leading to a name like "Wacom Serial Penabled 2FG Touchscreen
Pen".

Note that this drops BTN_TOOL_FINGER, it is not needed once the tools
are split out (and a touch device with BTN_TOOL_FINGER is interpreted
as touchpad by most of userspace).
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>