ARM: msm: Documentation: Add device tree binding for LLCC

Add documentation for LLCC (Last Level Cache Controller) device tree
bindings. This document provides overview of LLCC driver, device tree
binding for the LLCC driver and device tree binding for the clients that
use LLCC.

Change-Id: I28143053a7076eeb1991d85ebf80b7623ddd4368
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>