Input: wacom - add new Bamboo PT (0xdb)

Adds new Bamboo Pen & Touch model - Bamboo P & T Special Edition
Medium (CTH661/L; Product ID = 0xdb).

Tested-by: Tobias Verbeke <tobias.verbeke@gmail.com>
Signed-off-by: David Foley <favux.is@gmail.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>