nvc0: Enable ARB_shader_ballot on Kepler+

readInvocationARB() and readFirstInvocationARB() need SHFL.IDX
instruction which is introduced in Kepler.

Signed-off-by: Boyan Ding <boyan.j.ding@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
diff --git a/docs/features.txt b/docs/features.txt
index edc5684..a2d7785 100644
--- a/docs/features.txt
+++ b/docs/features.txt
@@ -292,7 +292,7 @@
   GL_ARB_sample_locations                               not started
   GL_ARB_seamless_cubemap_per_texture                   DONE (i965, nvc0, radeonsi, r600, softpipe, swr)
   GL_ARB_shader_atomic_counter_ops                      DONE (i965/gen7+, nvc0, radeonsi, softpipe)
-  GL_ARB_shader_ballot                                  DONE (radeonsi)
+  GL_ARB_shader_ballot                                  DONE (nvc0, radeonsi)
   GL_ARB_shader_clock                                   DONE (i965/gen7+, nv50, nvc0, radeonsi)
   GL_ARB_shader_draw_parameters                         DONE (i965, nvc0, radeonsi)
   GL_ARB_shader_group_vote                              DONE (nvc0, radeonsi)