ARM: dts: exynos: Enable CLKOUT on Exynos5410

The CLKOUT (which control is provided by PMU) is necessary for some of
the drivers using this as a clock, e.g. usb3503 USB HUB on Odroid XU
board.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>