We need to refer to the parent instead of the root BO for multi
level page tables on Vega10. Also don't set the PDE_PTE bit.

v2: Don't set the PDE_PTE bit either.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-and-Tested-by: Roger He <Hongbo.He@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>