ARM: dts: Update Samsung sysreg binding document

Added a binding example for reference and updated the
node name. While at it also removed the name description
as it is not necessary.

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>