HiresTextures: Support parsing DDS files directly

This leaves DDS textures using DXT1/3/5 compressed in-memory, which can
be passed directly to the backend.

Source/Core/VideoBackends/Software/SWmain.cpp

@@ -134,6 +134,7 @@ void VideoSoftware::InitBackendInfo()
   g_Config.backend_info.bSupportsComputeShaders = false;
   g_Config.backend_info.bSupportsInternalResolutionFrameDumps = false;
   g_Config.backend_info.bSupportsGPUTextureDecoding = false;
+  g_Config.backend_info.bSupportsST3CTextures = false;
 
   // aamodes
   g_Config.backend_info.AAModes = {1};