HID: wacom: Introduce new 'touch_input' device

Instead of having a single 'input_dev' device that will take either pen
or touch data depending on the type of the device, create seperate devices
devices for each. By splitting things like this, we can support devices
(e.g. the I2C "AES" sensors in some newer tablet PCs) that send both pen
and touch reports from a single endpoint.

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