Decode EFB copies used as paletted textures.

A number of games make an EFB copy in I4/I8 format, then use it as a
texture in C4/C8 format.  Detect when this happens, and decode the copy on
the GPU using the specified palette.

This has a few advantages: it allows using EFB2Tex for a few more games,
it, it preserves the resolution of scaled EFB copies, and it's probably a
bit faster.

D3D only at the moment, but porting to OpenGL should be straightforward..

Source/Core/VideoCommon/VertexManagerBase.cpp

@@ -209,6 +209,7 @@ void VertexManager::Flush()
 				if (bpmem.tevind[i].IsActive() && bpmem.tevind[i].bt < bpmem.genMode.numindstages)
 					usedtextures[bpmem.tevindref.getTexMap(bpmem.tevind[i].bt)] = true;
 
+		TextureCache::UnbindTextures();
 		for (unsigned int i : usedtextures)
 		{
 			g_renderer->SetSamplerState(i & 3, i >> 2);
@@ -224,6 +225,7 @@ void VertexManager::Flush()
 				ERROR_LOG(VIDEO, "error loading texture");
 			}
 		}
+		TextureCache::BindTextures();
 	}
 
 	// set global vertex constants