In the spirit of the codec split, this patch removes the documentation of
vaapidecode and adds a page per each possible decoder.
Nonetheless, only those available in the compilation system are going to be
instrospected, because the rest are not registered.
Trying to comply with GStreamer's element names, this patch renames the
encoders using the name format vaapi{codec}enc.
In this way, the plugin documentation is linked correctly.
Signed-off-by: Víctor Manuel Jáquez Leal <victorx.jaquez@intel.com>
