lavc: add a table of all codecs names.

The table is automatically generated from the definition of enum CodecID in
avcodec.h and contains the name of all known codecs, even those for which no
encoder nor decoder exists or is enabled.

The table is queried using the avcodec_get_name function.

If CONFIG_SMALL is true, the table is not compiled in; the avcodec_get_name
looks for names in the list of available decoders and encoders.