mov: use tkhd enabled flag to set the default track

Signed-off-by: Anton Khirnov <anton@khirnov.net>
movenc: Make tkhd "enabled" flag QuickTime compatible

QuickTime will play multiple audio tracks concurrently if this flag is
set for multiple audio tracks.  And if no subtitle track has this flag
set, QuickTime will show no subtitles in the subtitle menu.

Signed-off-by: Anton Khirnov <anton@khirnov.net>
vp56: Mark VP6-only optimizations as such.

Most of our VP56 optimizations are VP6-only and will stay that way.
So avoid compiling them for VP5-only builds.
libfdk-aacdec: formatting cosmetics
arm: h264chroma: Do not compile h264_chroma_mc* dependent on h264 decoder

The functions are used by all codecs that enable the h264chroma component
and the file is already compiled conditional on h264chroma being enabled.
h264_cabac: Mark functions calling decode_cabac_residual_internal as noinline

This ensures that decode_cabac_residual_internal actually does get inlined,
which it otherwise does not, even though it is marked as always_inline.