dnxhd: add better support for CIDs 1270 to 1274

These are DNxHR profiles with the following properties:
- Variable size in a profile (property added in a previous commit),
  requiring variable-sized macroblock table;
- Variable bitdepth, up to 12 bits.
- Better validation of buffer sizes and positions

Signed-off-by: Christophe Gisquet <christophe.gisquet@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
