These two fields are coded together into a single 16 bit integer with upper 8
bits for ext_mapping_idc and lower 8 bits for el_bit_depth_minus8.

Furthermore ext_mapping_idc has two components, upper 3 bits and lower 5 bits.
Co-authored-by: Niklas Haas <git@haasn.dev>
Signed-off-by: Niklas Haas <git@haasn.dev>