avcodec/rv10: Reduce the size of the tables used to initialize VLCs

avcodec/rv10: Reduce the size of the tables used to initialize VLCs

This can be achieved by switching to ff_init_vlc_from_lengths() which
allows to replace two uint16_t tables for codes with uint8_t tables for
the symbols by permuting the tables so that the codes are ordered from
left to right in the tree in which case they can be easily computed from
the lengths at runtime.

And after doing so, it became apparent that the tables for the symbols
are actually the same for luma and chroma, so that one can even omit one
of them.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>