x86/intel_rdt: Create resctrl debug area

In preparation for support of debugging of RDT sub features the user can
now enable a RDT debugfs region.

The debug area is always enabled when CONFIG_DEBUG_FS is set as advised in
http://lkml.kernel.org/r/20180523080501.GA6822@kroah.com



Also from same discussion in above linked email, no error checking on the
debugfs creation return value since code should not behave differently when
debugging passes or fails. Even on failure the returned value can be passed
safely to other debugfs calls.

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/9f553faf30866a6317f1aaaa2fe9f92de66a10d2.1529706536.git.reinette.chatre@intel.com