HID: wacom: EKR: have the wacom resources dynamically allocated

If we want to have one input device per remote, it's better to have our
own struct wacom_remote which is dynamically allocated.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>