llvmpipe nir fixes

This contains a set of fixes for the llvmpipe nir support. The last one removes the varyings fixup code from the state tracker, I can't find why this is needed anymore and it seems actively wrong, but I'd appreciate testing on radeonsi and some other platforms.

These add sysval front facing support to TGSI (it leaves support for face inputs as I'm not sure about the vmware state trackers), fixes point coord tests, some atomic crashes and finally all texcoord tests.

There are still a few regressions remaining in piglit, but it's only around 10.