ARM: dts: Update MFC DT binding documentation

Added an example for bindings for illustration and clarity.

Cc: devicetree-discuss@lists.ozlabs.org
Cc: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>