radeonsi: implement ARB_shader_group_vote

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
diff --git a/docs/features.txt b/docs/features.txt
index d707f01..1e145e1 100644
--- a/docs/features.txt
+++ b/docs/features.txt
@@ -295,7 +295,7 @@
   GL_ARB_shader_ballot                                  not started
   GL_ARB_shader_clock                                   DONE (i965/gen7+, radeonsi)
   GL_ARB_shader_draw_parameters                         DONE (i965, nvc0, radeonsi)
-  GL_ARB_shader_group_vote                              DONE (nvc0)
+  GL_ARB_shader_group_vote                              DONE (nvc0, radeonsi)
   GL_ARB_shader_stencil_export                          DONE (i965/gen9+, radeonsi, softpipe, llvmpipe, swr)
   GL_ARB_shader_viewport_layer_array                    DONE (i965/gen6+)
   GL_ARB_sparse_buffer                                  not started