xen: arm: propagate gic's #address-cells property to dom0.

xen: arm: propagate gic's #address-cells property to dom0.

The interrupt-map property requires that the interrupt-parent node
must have both #address-cells and #interrupt-cells properties (see
ePAPR 2.4.3.1). Therefore propagate the property if it is present.

We must propagate (rather than invent our own value) since this value
is used to size fields within other properties within the tree.

ePAPR strictly speaking requires that the interrupt-parent node
always has these properties. However reality has diverged from this
and implementations will recursively search parents for #*-cells
properties. Hence we only copy if it is present.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>