The configuration parameters seq_bounding_box_xyz0 and
seq_bounding_box_whd allow overriding the automatic derivation of
frame (sequence) bounding box, forcing the depth of the geometry
tree.

NB: seq_bounding_box_xyz0 and seq_bounding_box_whd are specified
    using unscaled co-ordinates.

NB: this patch does not signal these parameters in the SPS.