[D3D12] Fix DXN swizzle and cleanup texture swizzles

src/xenia/gpu/d3d12/texture_cache.h

@@ -266,13 +266,8 @@ class TextureCache {
     DXGI_FORMAT dxgi_format_resolve_tile;
     ResolveTileMode resolve_tile_mode;
 
-    // Whether the red component must be replicated in the SRV swizzle, for
-    // single-component formats. At least for DXT3A/DXT5A, this is according to
-    // http://fileadmin.cs.lth.se/cs/Personal/Michael_Doggett/talks/unc-xenos-doggett.pdf
-    // k_8 is also used with RGBA swizzle, but assumes replicated components, in
-    // Halo 3 sprites, thus it appears that all single-component formats should
-    // have RRRR swizzle.
-    bool replicate_component;
+    // Mapping of Xenos swizzle components to DXGI format components.
+    uint8_t swizzle[4];
   };
 
   union TextureKey {