TextureCache: Support compressed textures and pass pitch/size to upload

This also removes an extra copy of the image for custom textures.

Source/Core/VideoBackends/Null/NullBackend.cpp

@@ -45,6 +45,7 @@ void VideoBackend::InitBackendInfo()
   g_Config.backend_info.bSupportsMultithreading = false;
   g_Config.backend_info.bSupportsInternalResolutionFrameDumps = false;
   g_Config.backend_info.bSupportsGPUTextureDecoding = false;
+  g_Config.backend_info.bSupportsST3CTextures = false;
 
   // aamodes: We only support 1 sample, so no MSAA
   g_Config.backend_info.Adapters.clear();