arm64: dts: exynos: Move pmu and timer nodes out of soc

The ARM PMU and ARM architected timer nodes are part of ARM CPU design
therefore they should not be inside the soc node.  This also fixes DTC
W=1 warnings like:

    arch/arm64/boot/dts/exynos/exynos7.dtsi:472.11-480.5:
        Warning (simple_bus_reg): /soc/arm-pmu: missing or empty reg/ranges property
    arch/arm64/boot/dts/exynos/exynos7.dtsi:482.9-492.5:
        Warning (simple_bus_reg): /soc/timer: missing or empty reg/ranges property

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>