avcodec/internal: Move FF_CODEC_CAP_* to a new header codec_internal.h

Also move FF_CODEC_TAGS_END as well as struct AVCodecDefault.
This reduces the amount of files that have to include internal.h
(which comes with quite a lot of indirect inclusions), as e.g.
most encoders don't need it. It is furthemore in preparation
for moving the private part of AVCodec out of the public codec.h.

Signed-off-by: Andreas Rheinhardt <[email protected]>
diff --git a/libavcodec/mfenc.c b/libavcodec/mfenc.c
index 0430261..2f91e97 100644
--- a/libavcodec/mfenc.c
+++ b/libavcodec/mfenc.c
@@ -27,6 +27,7 @@
 #include "libavutil/imgutils.h"
 #include "libavutil/opt.h"
 #include "libavutil/time.h"
+#include "codec_internal.h"
 #include "internal.h"
 
 typedef struct MFContext {