dvenc: mark encoder as intra

And thus allow various multithreading.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dvenc.c

@@ -758,7 +758,7 @@ AVCodec ff_dvvideo_encoder = {
     .init           = dvvideo_encode_init,
     .encode2        = dvvideo_encode_frame,
     .close          = dvvideo_encode_close,
-    .capabilities   = CODEC_CAP_SLICE_THREADS,
+    .capabilities   = CODEC_CAP_SLICE_THREADS | CODEC_CAP_FRAME_THREADS | CODEC_CAP_INTRA_ONLY,
     .pix_fmts       = (const enum AVPixelFormat[]) {
         AV_PIX_FMT_YUV411P, AV_PIX_FMT_YUV422P,
         AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE