Show how the element size was calculated in the error message when a
'reg', 'ranges', or 'interrupts' property has the wrong size. This
should help with debugging. Also mention that #*-cells properties come
from the parent node, which can be subtle.
Came up in https://github.com/zephyrproject-rtos/zephyr/issues/21607
(though it seems the comment disappeared).
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>