ARM: dts: samsung: exynos4x12: replace duplicate pmu node with phandle

ARM: dts: samsung: exynos4x12: replace duplicate pmu node with phandle

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

The change is not compatible with older Linux kernel, which does not
parse samsung,pmu-syscon property.

Link: https://lore.kernel.org/r/20230722121719.150094-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>