PMU (system-controller@10040000) is used as interrupt-parent for certain
nodes thus it should be marked as interrupt-controller to silence
warnings when building Exynos5410-based DTBs:

  arch/arm/boot/dts/exynos5410-odroidxu.dtb: Warning (interrupts_property):
    Missing interrupt-controller or interrupt-map property in /soc/system-controller@10040000
  arch/arm/boot/dts/exynos5410-odroidxu.dtb: Warning (interrupts_property):
    Missing #interrupt-cells in interrupt-parent /soc/system-controller@10040000
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>