drm/amdgpu: enable RAS poison for VCN 2.6

Configure related settings to enable it.

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