drm/ttm: restructure to allow driver to plug in alternate memory manager

Nouveau will need this on GeForce 8 and up to account for the GPU
reordering physical VRAM for some memory types.

Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Acked-by: Thomas Hellström <thellstrom@vmware.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 267a86c..49b43c2 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -102,7 +102,8 @@
  */
 
 struct ttm_mem_reg {
-	struct drm_mm_node *mm_node;
+	void *mm_node;
+	unsigned long start;
 	unsigned long size;
 	unsigned long num_pages;
 	uint32_t page_alignment;