llvmpipe: enable PIPE_CAP_QUERY_PIPELINE_STATISTICS

This was implemented since forever, but not enabled.
It passes all piglit tests except one, arb_pipeline_statistics_query-frag.
The reason is that the test (for drawing a 10x10 rect) expects between
100 and 150 pixel shader invocations. But since llvmpipe counts this with
4x4 granularity (and due to the rect being 2 tris) we end up with 224
invocations. I believe however what llvmpipe is doing violates neither the
spirit nor the letter of the spec (our fragment shader granularity really
is 4x4 pixels, albeit we will bail out early on 2x2 or 4x2 (the latter
if AVX is available) granularity), the spec allows to count additional
invocations due to implementation reasons.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
diff --git a/docs/features.txt b/docs/features.txt
index 0435ce6..fe412f6 100644
--- a/docs/features.txt
+++ b/docs/features.txt
@@ -225,7 +225,7 @@
 
   GL_ARB_gl_spirv                                       in progress (Nicolai Hähnle, Ian Romanick)
   GL_ARB_indirect_parameters                            DONE (nvc0, radeonsi)
-  GL_ARB_pipeline_statistics_query                      DONE (i965, nvc0, radeonsi, softpipe, swr)
+  GL_ARB_pipeline_statistics_query                      DONE (i965, nvc0, radeonsi, llvmpipe, softpipe, swr)
   GL_ARB_polygon_offset_clamp                           DONE (i965, nv50, nvc0, r600, radeonsi, llvmpipe, swr)
   GL_ARB_shader_atomic_counter_ops                      DONE (i965/gen7+, nvc0, radeonsi, softpipe)
   GL_ARB_shader_draw_parameters                         DONE (i965, nvc0, radeonsi)