x86/intel_rdt: Add diagnostics when writing the cpus file

x86/intel_rdt: Add diagnostics when writing the cpus file

Can't add a cpu to a monitor group unless it belongs to parent
group. Can't delete cpus from the default group.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vikas Shivappa <vikas.shivappa@intel.com>
Cc: Boris Petkov <bp@suse.de>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lkml.kernel.org/r/757a869a25e9fc1b7a2e9bc43e1159455c1964a0.1506382469.git.tony.luck@intel.com