add hint to allow disabling the use of Xinput.

include/SDL_hints.h

@@ -196,6 +196,15 @@ extern "C" {
 #define SDL_HINT_ORIENTATIONS "SDL_IOS_ORIENTATIONS"
 
 
+/**
+ *  \brief  A variable that lets you disable the detection and use of Xinput gamepad devices
+ *
+ *  The variable can be set to the following values:
+ *    "0"       - Disable XInput timer (only uses direct input)
+ *    "1"       - Enable XInput timer (the default)
+ */
+#define SD_HINT_XINPUT_ENABLED "SDL_XINPUT_ENABLED"
+
 /**
  *  \brief  A variable that lets you manually hint extra gamecontroller db entries
  *