st/mesa: fix mipmap generation bug

In st_finalize_texture() we were looking at the st_texture_object::
lastLevel field instead of the pipe_resource::last_level field to
determine which resource to store the mipmap in.

Then, in st_generate_mipmap() we need to call st_finalize_texture() to
make sure the destination resource is properly allocated.

These changes fix the broken piglit fbo-generatemipmap-formats test.
(cherry picked from commit cae2bb76c1)

src/mesa/state_tracker/st_cb_texture.c

@@ -1852,8 +1852,9 @@ st_finalize_texture(GLcontext *ctx,
     * will match.
     */
    if (firstImage->pt &&
+       stObj->pt &&
        firstImage->pt != stObj->pt &&
-       firstImage->pt->last_level >= stObj->lastLevel) {
+       firstImage->pt->last_level >= stObj->pt->last_level) {
       pipe_resource_reference(&stObj->pt, firstImage->pt);
       pipe_sampler_view_reference(&stObj->sampler_view, NULL);
    }

src/mesa/state_tracker/st_gen_mipmap.c

@@ -366,6 +366,12 @@ st_generate_mipmap(GLcontext *ctx, GLenum target,
 
       pt = stObj->pt;
    }
+   else {
+      /* Make sure that the base texture image data is present in the
+       * texture buffer.
+       */
+      st_finalize_texture(ctx, st->pipe, texObj);
+   }
 
    assert(pt->last_level >= lastLevel);