x86/intel_rdt: Utilities to restrict/restore access to specific files

In support of Cache Pseudo-Locking we need to restrict access to specific
resctrl files to protect the state of a resource group used for
pseudo-locking from being changed in unsupported ways.

Introduce two utilities that can be used to either restrict or restore the
access to all files irrelevant to cache pseudo-locking when pseudo-locking
in progress for the resource group.

At this time introduce a new source file, intel_rdt_pseudo_lock.c, that
will contain most of the code related to cache pseudo-locking.

Temporarily mark these new functions as unused to silence compile warnings
until they are used.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/ab6319d1244366be3f9b7f9fba1c3da4810a274b.1529706536.git.reinette.chatre@intel.com