Input: wacom - update the ABI doc according to latest changes

Now the devices show up under hid no matter the connection (for USB
and Bluetooth, not serial nor i2c).

The USB devices can now be easily found under
/sys/bus/hid/devices/<bus>:<vid>:<pid>.<n>

The Bluetooth devices could also be found under this path since their
inclusion (April 2010), so this patch fixes the non-precise "hidraw*" path
for them.

The ABI has been unified while setting the LEDs and OLEDs. So Bluetooth
devices lost their own LED selector but use the USB sysfs attribute.
For OLEDs, Bluetooth devices handle only 1-bit images instead of 4 for USB.
The documentation has been updated to match this.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>