i965: implement ARB_pipeline_statistics_query

i965: implement ARB_pipeline_statistics_query

NOTE: The implementation was initially one patch, this. All the history is kept
here, even though all the core mesa changes were moved to the parent of this
patch.

This patch implements ARB_pipeline_statistics_query. This addition to GL does
not add a new API. Instead, it adds new tokens to the existing query APIs. The
work to hook up the new tokens is trivial due to it's similarity to the previous
work done for the query APIs. I've implemented all the new tokens to some
degree, but have stubbed out the untested ones at the entry point for Begin().
Doing this should allow the remainder of the code to be left in.

The new tokens give GL clients a way to obtain stats about the GL pipeline.
Generally, you get the number of things going in, invocations, and number of
things coming out, primitives, of the various stages. There are two immediate
uses for this, performance information, and debugging various types of
misrendering. I doubt one can use these for debugging very complex applications,
but for piglit tests, it should be quite useful.

Tessellation shaders, and compute shaders are not addressed in this patch
because there is no upstream implementation. I've implemented how I believe
tessellation shader stats will work for Intel hardware (though there is a bit of
ambiguity). Compute shaders are a bit more interesting though, and I don't yet
know what we'll do there.

For the lazy, here is a link to the relevant part of the spec:
https://www.opengl.org/registry/specs/ARB/pipeline_statistics_query.txt

Running the piglit tests
http://lists.freedesktop.org/archives/piglit/2014-November/013321.html
(http://cgit.freedesktop.org/~bwidawsk/piglit/log/?h=pipe_stats)
yield the following results:

> piglit-run.py -t stats tests/all.py output/pipeline_stats
> [5/5] pass: 5 Running Test(s): 5

v2:
- Don't allow pipeline_stats to be per stream (Ilia). This may (not sure) be
  needed for AMD_transform_feedback4, which we do not support.
   > If AMD_transform_feedback4 is supported then GEOMETRY_SHADER_PRIMITIVES_-
   > EMITTED_ARB counts primitives emitted to any of the vertex streams for
   > which STREAM_RASTERIZATION_AMD is enabled.
- Remove comment from GL3.txt because it is only used for extensions that are
  part of required versions (Ilia)
- Move the new tokens to a new XML doc instead of using the main GL4x.xml (Ilia)
- Add a fallthrough comment (Ilia)
- Only divide PS invocations by 4 on HSW+ (Ben)

v3:
- Add ARB_pipeline_statistics_query to relnotes.html
- Add ARB_pipeline_statistics_query.xml to the Makefile.am, and master XML (Ilia)
- Correct extension number (Ilia)
- Add link to xml in the main GL API xml (Ilia)
- remove special GS case from gen6_end_query (Ian)
- Make lookup table static so gcc doesn't initialized it on every call (Ian)
- Use if (_mesa_has_geometry_shaders(ctx)) instead of explicit checks (Ian)
- Core mesa parts moved into a prep patch (Ilia)

v4:
- Change to 10.6 relnotes since we missed 10.5 window
- Moved compute shader stuff into the switch statement (Jordan)
- Jordan: Add compute shader support

v5:
- Fixed relnote style (Ilia)

v6:
- Rebased on master which beat me to adding the first relnotes - essentially
  this undoes v5 (which had a typo anyway)
- Some code style fixes (Ken)
- Remove some excess comments (Ken)
- Unify tessellation failure style - unreachable (Ken)
- Fix workaround comment for PS invocations (Ken)

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>