Input: wacom - register an ac power supply for wireless devices

This is used by HID Bluetooth devices but also add some more information
to the USB Wireless Receiver.
We are just porting the bits from hid-wacom.c to the common driver here.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Przemo Firszt <przemo@firszt.eu>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>