ARM: dts: Document exynos5410 PMU

We will start using "samsung,exynos5410-pmu".
Signed-off-by: NAndreas Faerber <afaerber@suse.de>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>

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

@@ -7,6 +7,7 @@ Properties:
 		   - "samsung,exynos4212-pmu" - for Exynos4212 SoC,
 		   - "samsung,exynos4412-pmu" - for Exynos4412 SoC,
 		   - "samsung,exynos5250-pmu" - for Exynos5250 SoC,
+		   - "samsung,exynos5410-pmu" - for Exynos5410 SoC,
 		   - "samsung,exynos5420-pmu" - for Exynos5420 SoC.
 		second value must be always "syscon".