[Intel-gfx] R31 dithering

[Thomas Richter]

Hi Daniel, hi Ville,

thanks for your help. I used now the debug output to research how to 
enable dithering on the intel VCH. Apparently, it is bit #4 in register
VR01 that enables dithering. This is cross-checked by enabling in the
dvo_ivch.c file, which greatly improves image quality for 24bpp output. 
The bit itself is documented as "reserved" in the intel documentation, 
though it works quite nicely here.

I will now cross-check a little bit which other side effects this bit
has if combined with other DVO features (16bpp output, and scaler 
enabled). As soon as I have more, I'll prepare a small kernel patch for
it.

Thanks and have a nice weekend,

Thomas