x86/intel_rdt: Add tasks files

The root directory all subdirectories are automatically populated with a
read/write (mode 0644) file named "tasks". When read it will show all the
task IDs assigned to the resource group. Tasks can be added (one at a time)
to a group by writing the task ID to the file.  E.g.

Membership in a resource group is indicated by a new field in the
task_struct "int closid" which holds the CLOSID for each task. The default
resource group uses CLOSID=0 which means that all existing tasks when the
resctrl file system is mounted belong to the default group.

If a group is removed, tasks which are members of that group are moved to
the default group.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Cc: "Ravi V Shankar" <ravi.v.shankar@intel.com>
Cc: "Tony Luck" <tony.luck@intel.com>
Cc: "Shaohua Li" <shli@fb.com>
Cc: "Sai Prakhya" <sai.praneeth.prakhya@intel.com>
Cc: "Peter Zijlstra" <peterz@infradead.org>
Cc: "Stephane Eranian" <eranian@google.com>
Cc: "Dave Hansen" <dave.hansen@intel.com>
Cc: "David Carrillo-Cisneros" <davidcc@google.com>
Cc: "Nilay Vaish" <nilayvaish@gmail.com>
Cc: "Vikas Shivappa" <vikas.shivappa@linux.intel.com>
Cc: "Ingo Molnar" <mingo@elte.hu>
Cc: "Borislav Petkov" <bp@suse.de>
Cc: "H. Peter Anvin" <h.peter.anvin@intel.com>
Link: http://lkml.kernel.org/r/1477692289-37412-8-git-send-email-fenghua.yu@intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>