Add ff_ prefix to data symbols of encoders, decoders, hwaccel, parsers, bsf.

None of these symbols should be accessed directly, so declare them as
hidden.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit d36beb3f69)

libavcodec/rv10enc.c

@@ -56,7 +56,7 @@ void rv10_encode_picture_header(MpegEncContext *s, int picture_number)
     put_bits(&s->pb, 3, 0);     /* ignored */
 }
 
-AVCodec rv10_encoder = {
+AVCodec ff_rv10_encoder = {
     "rv10",
     AVMEDIA_TYPE_VIDEO,
     CODEC_ID_RV10,