Input: wacom_w8001 - split pen and touch initialization up

This is preparation work for splitting it up for two event nodes.

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>