ARM: dts: vfxxx: Move nodes which have no reg property out of bus

Move iio-hwmon node from soc node to root node.

iio-hwmon node does 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/vf500-colibri-eval-v3.dtb: Warning (simple_bus_reg): Node /soc/iio-hwmon missing or empty reg/ranges property

Based on a patch from Simon Horman for the renesas r8a7795 dtsi.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>