Input: xpad - set the LEDs properly on XBox Wireless controllers

Based on Patch by Pierre-Loup A. Griffais <pgriffais@valvesoftware.com>:
Add the logic to set the LEDs on XBox Wireless controllers.  Command
sequence found by sniffing the Windows data stream when plugging the
device in.

Updated based on comments on linux-input:
unify codepaths in xpad_send_led_command for wired/ wireless controller.
Also document command values for clarification.
All values tested on Xbox 360 Wireless Controller.

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