media: exynos4-is: fimc-is: replace duplicate pmu node with phandle

Devicetree for the FIMC IS camera included duplicated PMU node as its
child like:

  soc@0 {
    system-controller@10020000 { ... }; // Real PMU

    camera@11800000 {
      fimc-is@12000000 {
        // FIMC IS camera node
        pmu@10020000 {
          reg = <0x10020000 0x3000>; // Fake PMU node
        };
      };
    };
  };

This is not a correct representation of the hardware.  Mapping the PMU
(Power Management Unit) IO memory should be via syscon-like phandle
(samsung,pmu-syscon, already used for other drivers), not by duplicating
"pmu" Devicetree node inside the FIMC IS.  Backward compatibility is
preserved.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>