lavc: restore copy_block{4,16} functions

They were removed in 9e31729d692f1e721b7ed1a3a0f51b68c064d68f.
LucasArts SMUSH SANM video decoder

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
LucasArts SMUSH VIMA audio decoder

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
LucasArts SMUSH demuxer

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
fate: add tests for SANM and VIMA

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>