dt-bindings: Add DT bindings for specifying the count factor

This patch adds the DT bindings to specify a property that
indicates the number of bytes the monitor counts in
so we can properly scale the count we read from the hardware to
reflect the traffic.

Change-Id: I7b3819b3849faff34ee6aa4cf8133df7d46f1bfb
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>