Input: xpad - x360w: report dpad as buttons and axes

Input: xpad - x360w: report dpad as buttons and axes

as discussed here[0], x360w is the only pad that maps dpad_to_button.
This is bad for downstream developers as they have to differ between
x360 and x360w which is not intuitive.

This patch implements the suggested solution of exposing the dpad both
as axes and as buttons. This retains backward compatibility with software
already dealing with the difference while makes new software work as
expected across x360/ x360w pads.

[0] http://www.spinics.net/lists/linux-input/msg34421.html

Signed-off-by: Pavel Rojtberg <rojtberg@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>