avcodec/mpc8: Reduce size of tables used to initialize VLCs

avcodec/mpc8: Reduce size of tables used to initialize VLCs

By switching to ff_init_vlc_from_lengths() one can make a table of
codes of type uint8_t superfluous, saving space.

Other VLCs (those without dedicated symbols table and with codes of
type uint8_t) have been made to use ff_init_vlc_from_lengths(), too,
because it reduces codesize (ff_init_vlc_from_lengths() has two
parameters less than ff_init_vlc_sparse()) and because it allows to
use the offset parameter in future commits.

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