Move pmu, usbphy0 and usbphy1 nodes from soc node to root node.

The nodes that have been moved do not have any register properties and thus
shouldn't be placed on the bus.

This fixes the following build warnings with W=1:

arch/arm/boot/dts/imx53-ard.dtb: Warning (unit_address_vs_reg): Node /memory has a reg or ranges property, but no unit name
arch/arm/boot/dts/imx53-ard.dtb: Warning (simple_bus_reg): Node /soc/aips@50000000/usbphy-0 missing or empty reg/ranges property
arch/arm/boot/dts/imx53-ard.dtb: Warning (simple_bus_reg): Node /soc/aips@50000000/usbphy-1 missing or empty reg/ranges property
arch/arm/boot/dts/imx53-ard.dtb: Warning (simple_bus_reg): Node /soc/pmu missing or empty reg/ranges property

Based on a patch from Simon Horman for r8a7795.dtsi.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>