drm/amdgpu: unbind in amdgpu_ttm_tt_unpopulate

Doing this in amdgpu_ttm_backend_destroy() is to late.

It turned out that this is not a good idea at all because it leaves pointers
to freed up system memory pages in the GART tables of the drivers.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728130552.2074-2-christian.koenig@amd.com

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -1066,7 +1066,6 @@ static void amdgpu_ttm_backend_destroy(struct ttm_device *bdev,
 {
 	struct amdgpu_ttm_tt *gtt = (void *)ttm;
 
-	amdgpu_ttm_backend_unbind(bdev, ttm);
 	ttm_tt_destroy_common(bdev, ttm);
 	if (gtt->usertask)
 		put_task_struct(gtt->usertask);
@@ -1148,6 +1147,8 @@ static void amdgpu_ttm_tt_unpopulate(struct ttm_device *bdev,
 	struct amdgpu_ttm_tt *gtt = (void *)ttm;
 	struct amdgpu_device *adev;
 
+	amdgpu_ttm_backend_unbind(bdev, ttm);
+
 	if (gtt && gtt->userptr) {
 		amdgpu_ttm_tt_set_user_pages(ttm, NULL);
 		kfree(ttm->sg);