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>

Documentation/devicetree/bindings/arm/samsung/sysreg.txt

 SAMSUNG S5P/Exynos SoC series System Registers (SYSREG)
 
 Properties:
- - name : should be 'sysreg';
  - compatible : should contain "samsung,<chip name>-sysreg", "syscon";
    For Exynos4 SoC series it should be "samsung,exynos4-sysreg", "syscon";
  - reg : offset and length of the register set.
+
+Example:
+	syscon@10010000 {
+		compatible = "samsung,exynos4-sysreg", "syscon";
+		reg = <0x10010000 0x400>;
+	};