Update SDL2 to newest version to fix 7.1 playback

This fixes 7.1 playback. Before this commit, SDL used 7.1 front audio configuration with Center Left and Center Right speakers, but without Rear speakers.

See https://github.com/libsdl-org/SDL/issues/11709 for more details.

libs/SDL2/include/SDL_power.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -23,9 +23,9 @@
 #define SDL_power_h_
 
 /**
- *  \file SDL_power.h
+ * # CategoryPower
  *
- *  Header for the SDL power management routines.
+ * Header for the SDL power management routines.
  */
 
 #include "SDL_stdinc.h"
@@ -37,9 +37,9 @@ extern "C" {
 #endif
 
 /**
- *  The basic state for the system's power supply.
+ * The basic state for the system's power supply.
  */
-typedef enum
+typedef enum SDL_PowerState
 {
     SDL_POWERSTATE_UNKNOWN,      /**< cannot determine power status */
     SDL_POWERSTATE_ON_BATTERY,   /**< Not plugged in, running on the battery */
@@ -66,10 +66,10 @@ typedef enum
  *
  * \param seconds seconds of battery life left, you can pass a NULL here if
  *                you don't care, will return -1 if we can't determine a
- *                value, or we're not running on a battery
+ *                value, or we're not running on a battery.
  * \param percent percentage of battery life left, between 0 and 100, you can
  *                pass a NULL here if you don't care, will return -1 if we
- *                can't determine a value, or we're not running on a battery
+ *                can't determine a value, or we're not running on a battery.
  * \returns an SDL_PowerState enum representing the current battery state.
  *
  * \since This function is available since SDL 2.0.0.