drm/amdgpu: store PA with column bits cleared for RAS bad page

So the code can be simplified, and no need to expose the detail of PA
format outside address conversion.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>