vd_lavc: add d3d11va hwdec

This commit adds the d3d11va-copy hwdec mode using the ffmpeg d3d11va
api. Functions in common with dxva2 are handled in a separate decode/d3d.c
file. A future commit will rewrite decode/dxva2.c to share this code.

video/fmt-conversion.c

@@ -109,6 +109,9 @@ static const struct {
 #endif
     {IMGFMT_VAAPI, AV_PIX_FMT_VAAPI_VLD},
     {IMGFMT_DXVA2, AV_PIX_FMT_DXVA2_VLD},
+#if HAVE_D3D11VA_HWACCEL
+    {IMGFMT_D3D11VA, AV_PIX_FMT_D3D11VA_VLD},
+#endif
 #if HAVE_AV_PIX_FMT_MMAL
     {IMGFMT_MMAL, AV_PIX_FMT_MMAL},
 #endif