docs/plugins/: Update docs with caps info.

docs/plugins/: Update docs with caps info.

Original commit message from CVS:
* docs/plugins/gst-plugins-ugly-plugins.args:
* docs/plugins/inspect/plugin-a52dec.xml:
* docs/plugins/inspect/plugin-amrnb.xml:
* docs/plugins/inspect/plugin-asf.xml:
* docs/plugins/inspect/plugin-dvdlpcmdec.xml:
* docs/plugins/inspect/plugin-dvdread.xml:
* docs/plugins/inspect/plugin-dvdsub.xml:
* docs/plugins/inspect/plugin-iec958.xml:
* docs/plugins/inspect/plugin-lame.xml:
* docs/plugins/inspect/plugin-mad.xml:
* docs/plugins/inspect/plugin-mpeg2dec.xml:
* docs/plugins/inspect/plugin-mpegaudioparse.xml:
* docs/plugins/inspect/plugin-mpegstream.xml:
Update docs with caps info.