Add \since docs where missing and resets some to 3.0.0

- remove a \returns

include/SDL3/SDL_atomic.h

@@ -186,6 +186,10 @@ extern __inline void SDL_CompilerBarrier(void);
  * \since This function is available since SDL 3.0.0.
  */
 extern DECLSPEC void SDLCALL SDL_MemoryBarrierReleaseFunction(void);
+
+/*
+ * \since This function is available since SDL 3.0.0.
+ */
 extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquireFunction(void);
 
 #if defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))