Make sure that libgstvaapi private headers remain internally used to
build libgstvaapi libraries only. All header dependencies were reviewed
and checks for IN_LIBGSTVAAPI definition were added accordingly.
Also rename GST_VAAPI_CORE definition to IN_LIBGSTVAAPI_CORE to keep
consistency.
Fix default CPB buffer size to something more reasonable (1500 ms)
and that still fits the level limits. This is a non configurable
property for now. The initial CPB removal delay is also fixed to
750 ms.
https://bugzilla.gnome.org/show_bug.cgi?id=722087
Instal <gst/vaapi/gstvaapiutils_h264.h> header but only expose the
H.264 levels in there. The additional helper functions are meant
to be private for now.
