Input: wacom - install LED/OLED sysfs files in the HID device instead of USB

Removes one more dependency over USB, but requires some changes in
the user space to find the sysfs files correctly.

This patch breaks the user space. However, the number of program
accessing the LEDs is quite limited and we can easily patch them
to handle the new HID behavior.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Jason Gerecke <killertofu@gmail.com>
Tested-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>