HID: wacom: Support devices with two touchrings

If a device has more than one touchring, we want to be sure that userspace
is able to distinguish them. Following previous standards, the first
absolute ring will be reported as ABS_WHEEL and the second as ABS_THROTTLE.
Relative rings will use REL_WHEEL_HI_RES / REL_WHEEL for the first and
REL_HWHEEL_HI_RES / REL_HWHEEL for the second.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>