HID: wacom: Add support for Cintiq Companion 2

Adds support for the EMR (pen+pad) and touchscreen devices used by the
Wacom Cintiq Companion 2. This applies both to using the device as a
standalone system, as well as when operating in "Cintiq mode" (where
the EMR/touchscreen are simply exposed as USB devices to the system
its connected to).

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Clifford Jolly <expiredpopsicle@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>