Move copy.{c,h} from module avcodec to module video_chroma.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
intf: WebVTT extensions detection

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
MediaCodec: use SSE copy function from the avcodec module if the CPU supports it.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>