AAC packetizer: deindent state machine switch
AAC packetizer: move functions around file
AAC packetizer: comment write-only arrays
Fix Duck DK3/DK4 ADPCM mappings

Also give them VLC_CODEC_ names and use them in the adpcm decoder.

v2: Add codec description strings

Signed-off-by: Rafaël Carré <funman@videolan.org>