x86/intel_rdt/mba_sc: Documentation for MBA software controller(mba_sc)

Add documentation about the feedback loop mechanism (MBA software
controller) which lets the user specify the memory bandwidth allocation
in MBps. This includes some changes to "schemata" formati with
examples.

Signed-off-by: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: ravi.v.shankar@intel.com
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: vikas.shivappa@intel.com
Cc: ak@linux.intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/1524263781-14267-2-git-send-email-vikas.shivappa@linux.intel.com