Input: xpad - add support for SteelSeries Stratus Duo

Add support for the SteelSeries Stratus Duo, a wireless Xbox 360
controller. The Stratus Duo ships with a USB dongle to enable wireless
connectivity, but it can also function as a wired controller by connecting
it directly to a PC via USB, hence the need for two USD PIDs. 0x1430 is the
dongle, and 0x1431 is the controller.

Signed-off-by: Tom Panfil <tom@steelseries.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>