[Intel-gfx] Manual control of LVDS pixel formats and dual channel mode

[Chris Wilson]

Mike, I wasn't keen on introducing this option to disable the LVDS fixed
mode. I think we want to allow the user to specify the fixed mode to use
instead, without the intermediate stop-gap solution of completely disabling
the probe. Later we can extend that ability (if possible or still desirable
on reflection) so that we can specify all the LVDS configuration options
in the single string.

But first can you check that I've correctly forward ported your other
patches on top of Eric's refactoring.

Many thanks,
-Chris