Add and update include guards

Include guards in most changed files were missing, I added them keeping
the same style as other SDL files. In some cases I moved the include
guards around to be the first thing the header has to take advantage of
any possible improvements compiler may have for inclusion guards.

src/joystick/steam/SDL_steamcontroller.h

@@ -18,6 +18,10 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+#ifndef SDL_steamcontroller_h_
+#define SDL_steamcontroller_h_
+
 #include "../../SDL_internal.h"
 
 typedef SDL_bool (*SteamControllerConnectedCallback_t)(const char *name, SDL_JoystickGUID guid, int *device_instance);
@@ -30,4 +34,6 @@ void SDL_UpdateSteamControllers(void);
 void SDL_UpdateSteamController(SDL_Joystick *joystick);
 void SDL_QuitSteamControllers(void);
 
+#endif /* SDL_steamcontroller_h_ */
+
 /* vi: set ts=4 sw=4 expandtab: */