Input: xpad - power off wireless 360 controllers on suspend

When the USB wireless adapter is suspended, the controllers
lose their connection. This causes them to start flashing
their LED rings and searching for the wireless adapter
again, wasting the controller's battery power.

Instead, we will tell the controllers to power down when
we suspend. This mirrors the behavior of the controllers
when connected to the console itself and how the official
Xbox One wireless adapter behaves on Windows.

Signed-off-by: Cameron Gutman <aicommander@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>