configure.in: Make SDL depend on joystick, TexturePacker or Apple

Currently, when using --disable-sdl, the Joystick support is still enabled by default. This leads to
```
CPP     xbmc/input/ButtonTranslator.o
In file included from ButtonTranslator.cpp:44:0:
SDLJoystick.h:51:31: fatal error: SDL2/SDL_joystick.h: No such file or directory
```

This patch remove the disable-sdl switch. Instead, SDL is required
whenever joystick support is enabled, TexturePacker is enabled or when
building on apple.
If joystick support and TexturePacker is left on auto (as it is the
default), they are enabled when SDL is detected and disabled if no SDL
is detected.