intel: make intel_texture_image a subclass of swrast_texture_image

We need to subclass swrast_texture_image because if we use swrast for
fallback rendering, we'll need to have swrast_texture_image objects.

src/mesa/drivers/dri/intel/intel_fbo.c

@@ -611,8 +611,8 @@ intel_renderbuffer_set_draw_offset(struct intel_renderbuffer *irb,
 
    /* compute offset of the particular 2D image within the texture region */
    intel_miptree_get_image_offset(intel_image->mt,
-				  intel_image->base.Level,
-				  intel_image->base.Face,
+				  intel_image->base.Base.Level,
+				  intel_image->base.Base.Face,
 				  zoffset,
 				  &dst_x, &dst_y);
 
@@ -738,18 +738,18 @@ intel_render_texture(struct gl_context * ctx,
       struct intel_mipmap_tree *new_mt;
 
       new_mt = intel_miptree_create(intel, image->TexObject->Target,
-				    intel_image->base.TexFormat,
-				    intel_image->base.Level,
-				    intel_image->base.Level,
-				    intel_image->base.Width,
-				    intel_image->base.Height,
-				    intel_image->base.Depth,
+				    intel_image->base.Base.TexFormat,
+				    intel_image->base.Base.Level,
+				    intel_image->base.Base.Level,
+				    intel_image->base.Base.Width,
+				    intel_image->base.Base.Height,
+				    intel_image->base.Base.Depth,
 				    GL_TRUE);
 
       intel_miptree_image_copy(intel,
                                new_mt,
-			       intel_image->base.Face,
-			       intel_image->base.Level,
+			       intel_image->base.Base.Face,
+			       intel_image->base.Base.Level,
 			       old_mt);
 
       intel_miptree_release(intel, &intel_image->mt);