drm/vram: switch to gem vma offset manager

Pass gem vma_offset_manager to ttm_bo_device_init(), so ttm uses it
instead of its own embedded struct.  This makes some gem functions
(specifically drm_gem_object_lookup) work on ttm objects.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20190905070509.22407-4-kraxel@redhat.com

drivers/gpu/drm/drm_vram_mm_helper.c

@@ -228,7 +228,7 @@ int drm_vram_mm_init(struct drm_vram_mm *vmm, struct drm_device *dev,
 
 	ret = ttm_bo_device_init(&vmm->bdev, &bo_driver,
 				 dev->anon_inode->i_mapping,
-				 NULL,
+				 dev->vma_offset_manager,
 				 true);
 	if (ret)
 		return ret;