st/mesa: enable GL_KHR_robustness

The difference to the virtually identical ARB_robustness (which is already
enabled unconditionally) is miniscule and handled elsewhere, but this cap
seems like the right thing to require for this extension.

v2: drop the device reset cap requirement (Ilia)

Reviewed-by: Marek Olšák <marek.olsak@amd.com> (v1)
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>

docs/features.txt

@@ -218,7 +218,7 @@ GL 4.5, GLSL 4.50:
   GL_ARB_shader_texture_image_samples                   DONE (i965, nv50, nvc0, r600, radeonsi)
   GL_ARB_texture_barrier                                DONE (i965, nv50, nvc0, r600, radeonsi)
   GL_KHR_context_flush_control                          DONE (all - but needs GLX/EGL extension to be useful)
-  GL_KHR_robustness                                     DONE (i965)
+  GL_KHR_robustness                                     DONE (i965, nvc0, radeonsi)
   GL_EXT_shader_integer_mix                             DONE (all drivers that support GLSL)
 
 These are the extensions cherry-picked to make GLES 3.1

docs/relnotes/12.1.0.html

@@ -60,6 +60,7 @@ Note: some of the new features are only available with certain drivers.
 <li>GL_ARB_texture_stencil8 on i965/hsw</li>
 <li>GL_EXT_window_rectangles on nv50, nvc0</li>
 <li>GL_KHR_blend_equation_advanced on i965</li>
+<li>GL_KHR_robustness on nvc0, radeonsi</li>
 <li>GL_KHR_texture_compression_astc_sliced_3d on i965</li>
 <li>GL_OES_copy_image on nv50, nvc0, r600, radeonsi, softpipe, llvmpipe</li>
 <li>GL_OES_geometry_shader on i965/gen8+, nvc0, radeonsi</li>

src/mesa/state_tracker/st_extensions.c

@@ -1199,6 +1199,8 @@ void st_init_extensions(struct pipe_screen *screen,
       }
    }
 
+   extensions->KHR_robustness = extensions->ARB_robust_buffer_access_behavior;
+
    /* If we support ES 3.1, we support the ES3_1_compatibility ext. However
     * there's no clean way of telling whether we would support ES 3.1 from
     * here, so copy the condition from compute_version_es2 here. A lot of