[Mesa-dev] Resend V4 ARB_enhanced_layouts packing support for i965 Gen6+

[Timothy Arceri]

This is just a resend that is rebased and has previously reviewed patches pushed to master.

V4:
 - add vec4 backend support and enable for Gen6+
 
 V3:
- Rewrite patch 9 (add support for packing arrays) to not add
 hacks to the type_size() functions.
 - Add packing support for the load_output intrinsics (patch 12)
 - Add glsl_dvec_type() helper (patch 8)
 
 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 Gen6+.
 
 Series can be found in my component_packing_gen6+ branch:
 
 https://github.com/tarceri/Mesa_arrays_of_arrays.git