selftests/resctrl: Use cache index3 id for AMD schemata masks

AMD uses the cache l3 boundary for schemata masks. Update it accordigly.

Signed-off-by: Babu Moger <babu.moger@amd.com>
Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>