#R600 shader from NIR

This code is an attempt to implement a NIR backend for r600.

Supported hardware: Cayman, Evergreen and NI (tested on CAYMAN, CEDAR and BARTS)

Thanks to soft fp64 the OpenGL version is now 4.5 also for EG.

sb can bee enabled for nir, it still gives some improvements, e.g. with Xonotic
The aim is still to get rid of it.


## State

TODO:

piglits gpu passes mostly like with TGSI, there are some fixes but also a few regressions.

piglit:
  * spilling arrays is broken on Barts and CAYMAN (but it works on Cedar)

## Needed optimizations:

  - peepholes:
    - compare + set predicate / kill
  - use clause local registers
  - reduce register usage
  - don't rely on the backend to schedule addr load and Index load as well
  - don't rely on the backend to merge some alu groups

## There are still some hangs
