Fix SDL_GameController API for PSP (#3)

- Add missing mapping
- Make sure the only window has the keyboard focus (so no `SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS` is needed)

src/video/psp/SDL_pspvideo.c

@@ -214,6 +214,7 @@ PSP_CreateWindow(_THIS, SDL_Window * window)
     /* Setup driver data for this window */
     window->driverdata = wdata;
 
+    SDL_SetKeyboardFocus(window);
 
     /* Window has been successfully created */
     return 0;