st/mesa: only expose ARB_shader_bit_encoding with GLSL 1.3

I don't think it's possible or even useful to use the extension with GLSL 1.2.
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_extensions.c

@@ -578,6 +578,7 @@ void st_init_extensions(struct st_context *st)
 
       /* Extensions that only depend on GLSL 1.3. */
       ctx->Extensions.ARB_conservative_depth = GL_TRUE;
+      ctx->Extensions.ARB_shader_bit_encoding = GL_TRUE;
    } else {
       /* Optional integer support for GLSL 1.2. */
       if (screen->get_shader_param(screen, PIPE_SHADER_VERTEX,
@@ -595,10 +596,6 @@ void st_init_extensions(struct st_context *st)
       ctx->Extensions.S3_s3tc = GL_FALSE;
    }
 
-   if (ctx->Const.NativeIntegers) {
-      ctx->Extensions.ARB_shader_bit_encoding = GL_TRUE;
-   }
-
    if (screen->get_shader_param(screen, PIPE_SHADER_GEOMETRY,
                                 PIPE_SHADER_CAP_MAX_INSTRUCTIONS) > 0) {
 #if 0 /* XXX re-enable when GLSL compiler again supports geometry shaders */