[FFmpeg-soc] DCA encoder fixes

Here's proof of the concept patch to the dcaenc.c which fixes DCA encoding. It is not very clean and should be splitted into parts. Spotted and fixed/workarounded bugs: * avctx->frame_size was unset with filling temp buffer instead * small errors in bistream writing * no check was done on written data - outputting 0xFFFF in bitstream may be treated as syncword so I clear last bit of quantized value (so it can't be made from to consequent words as well). And I'd like to do AAC encoder anyway.