avcodec/asvenc: Avoid reversing output data twice

avcodec/asvenc: Avoid reversing output data twice

The ASUS V2 format is designed for a little-endian bitstream reader, yet
our encoder used an ordinary big-endian bitstream writer to write it;
the bits of every byte were swapped at the end and some data (namely the
numbers not in static tables) had to be bitreversed before writing it at
all, so that it would be reversed twice.

This commit stops doing so; instead, a little-endian bitstream writer is
used. This also necessitated to switch certain static tables, which
required trivial modifications to the decoder (that uses the same
tables).

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>