[SDL] Add global helper to setup the library.

Call to SDLHelper::Prepare() is needed before first SDL_InitSubSystem().
- Sets hints (SDL configuration vars).
- Configures logging.

src/xenia/apu/sdl/premake5.lua

@@ -7,8 +7,9 @@ project("xenia-apu-sdl")
   kind("StaticLib")
   language("C++")
   links({
-    "xenia-base",
     "xenia-apu",
+    "xenia-base",
+    "xenia-helper-sdl",
     "SDL2",
   })
   defines({