Add KHR_display extension to v3dv

Hi,

I'm interested in getting KHR_display working in v3dv.

Implementations for other platforms (such as 451b58a5) appear to be fairly straightforward. Would this be correct or is it likely there's something missing in the (very recently merged) v3dv driver?

I'm willing to attempt this myself but it's slightly out of my comfort zone and would largely be copy and pasting the above commit. My main question is: is this likely to work or is there a lot more to it?

EDIT: by copy and paste, I mean like this: dmrlawson/mesa@7af4e7a8 (not tested it even builds yet)