Hub nodes and host-controller nodes with child nodes must specify values
for #address-cells (1) and #size-cells (0).

Also make the definition of the related reg property a bit more
stringent, and add comments to the example source.
Signed-off-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NRob Herring <robh@kernel.org>