HID: wacom: generic: add mode change touch key

Wacom Cintiq Pro added a touch key to switch the tablet between
display and opaque mode. This patch informs the change by removing
the old devices and creating new ones with proper properties.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Ping Cheng <ping.cheng@wacom.com>
Tested-by: Aaron Armstrong Skomra <aaron.skomra@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>