gallium: implement ARB_texture_query_levels

The extension is always supported if GLSL 1.30 is supported.

Softpipe and llvmpipe support is also added (trivial).
Radeon and nouveau support is already done.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

docs/relnotes/10.3.html

@@ -50,6 +50,7 @@ Note: some of the new features are only available with certain drivers.
 <li>GL_ARB_stencil_texturing on nv50, nvc0, r600, and radeonsi</li>
 <li>GL_ARB_texture_cube_map_array on radeonsi</li>
 <li>GL_ARB_texture_gather on radeonsi</li>
+<li>GL_ARB_texture_query_levels on nv50, nvc0, llvmpipe, r600, radeonsi, softpipe</li>
 <li>GL_ARB_viewport_array on nvc0</li>
 </ul>