codec: bitpacked: add decoder

codec: bitpacked: add decoder

Add a codec capable of decoding some formats of the RFC4175. For now
it's only capable of handling YCbCr-4:2:2 with 8-bit or 10-bit depth.

For 8-bit it's a simple pass-through, for 10-bit it depacks the stream
in the AV_PIX_FMT_YUV422P10 pixel format.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>