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/pnmenc.c

@@ -113,7 +113,7 @@ static int pnm_encode_frame(AVCodecContext *avctx, unsigned char *outbuf,
 
 
 #if CONFIG_PGM_ENCODER
-AVCodec pgm_encoder = {
+AVCodec ff_pgm_encoder = {
     "pgm",
     AVMEDIA_TYPE_VIDEO,
     CODEC_ID_PGM,
@@ -126,7 +126,7 @@ AVCodec pgm_encoder = {
 #endif
 
 #if CONFIG_PGMYUV_ENCODER
-AVCodec pgmyuv_encoder = {
+AVCodec ff_pgmyuv_encoder = {
     "pgmyuv",
     AVMEDIA_TYPE_VIDEO,
     CODEC_ID_PGMYUV,
@@ -139,7 +139,7 @@ AVCodec pgmyuv_encoder = {
 #endif
 
 #if CONFIG_PPM_ENCODER
-AVCodec ppm_encoder = {
+AVCodec ff_ppm_encoder = {
     "ppm",
     AVMEDIA_TYPE_VIDEO,
     CODEC_ID_PPM,
@@ -152,7 +152,7 @@ AVCodec ppm_encoder = {
 #endif
 
 #if CONFIG_PBM_ENCODER
-AVCodec pbm_encoder = {
+AVCodec ff_pbm_encoder = {
     "pbm",
     AVMEDIA_TYPE_VIDEO,
     CODEC_ID_PBM,