DRM/KMS: vmwgfx driver is now available

[PHO <pho%cielonegro.org@localhost>]

Hi,

I've been working on vmwgfx driver, a driver for VMware virtualized GPU. 
It was partly ported to NetBSD but wasn't buildable, and now it builds 
and actually works. (Thank you riastradh@, your prior work helped 
tremendously. I don't think I could do this without it.)

This is the list of patches I'd like to commit:
https://github.com/NetBSD/src/compare/trunk...depressed-pho:netbsd-src:drm2-vmwgfx

Here's what I tested:

- benchmarks/glmark2 completes without crashing, and it tells me that 
the virtual GPU is 37x better than software rasterization.

- wm/compiz seems to work, but since I had no prior experiences there 
might be broken things I didn't realize.

- "picom --backend glx" works flawlessly in combination with wm/fluxbox.

- x11/enlightenment works, but I don't know if it actually uses GLX.

Note that you need to update your pkgsrc tree to try the driver, as I 
fixed a few things that needed fixing. Also the base X.org is not 
capable of making use of the driver because its Mesa is built without 
libxatracker. You need the modular one from pkgsrc.