ARM: dts: Enable PRNG module on exynos4412-trats2

Enable Pseudo Random Number Generator (PRNG) on Trats2 board. This
allows using hardware random number generator:
$ echo exynos > /sys/class/misc/hw_random/rng_current

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