mlpenc: Working MLP/TrueHD encoder

* Multichannel support for TrueHD is experimental

    There should be downmix substreams present for 2+ channel bitstreams,
    but ffmpeg decoder doesn't need it. Will add support for this soon.

* There might be lossless check failures on LFE channels

* 32-bit sample support has been removed for now, will add it later

    While testing, some samples gave lossless check failures when enforcing
    s32. Probably this will also get solved with the LFE issues.

Signed-off-by: Jai Luthra <me@jailuthra.in>
