[Nouveau] DCB 4.1 spec update

[Andy Ritger]

Hi,

The VBIOS on GM20x GPUs uses a slightly updated version of the DCB.
I've posted an updated DCB spec here:

ftp://download.nvidia.com/open-gpu-doc/DCB/2/DCB-4.x-Specification.html

You can diff it against the previous version:

ftp://download.nvidia.com/open-gpu-doc/DCB/1/DCB-4.0-Specification.html

to see what changed (sorry for having to diff html files).  The biggest
differences are Serial Output Resource (SOR) assignment, and the updated
Communications Control Block layout.

I hope that is helpful,
- Andy