HID: wacom: remove hardcoded WACOM_QUIRK_MULTI_INPUT

The quirk was added for devices that support both pen and touch.  It decides if
a device supports multiple inputs by hardcoded feature type. However, for some
devices, we do not know if they support both before accessing their HID
descriptors.

This patch relies on dynamically assigned device_type to make the decision.
Also, we make it certain that wacom_wac->shared is always created. That is, the
driver will not be loaded if it fails to create wacom_wac->shared.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>