HID: hid-oxp: Add Second Generation Gamepad Mode Switch

HID: hid-oxp: Add Second Generation Gamepad Mode Switch

Adds "gamepad_mode" attribute to second generation OneXPlayer
configuration HID devices. This attribute initiates a mode shift in the
device MCU that puts it into a state where all events are routed to an
hidraw interface instead of the xpad evdev interface. This allows for
debugging the hardware input mapping added in the next patch.

Reviewed-by: Zhouwang Huang <honjow311@gmail.com>
Tested-by: Zhouwang Huang <honjow311@gmail.com>
Signed-off-by: Derek J. Clark <derekjohn.clark@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>