[Mesa-dev] V2 ARB_enhanced_layouts packing support for i965 Gen8+

[Timothy Arceri]

V2:
- validation fixes patches 1-2
- added support for packing doubles now that explicit location
 fixes have landed.
- fix various issues with intel debug output with new COMPONENT const index.

This adds component packing support for Gen8+.

Series can be found in my component_packing_backend4 branch:

https://github.com/tarceri/Mesa_arrays_of_arrays.git