arm64/xen: Add missing #address-cells and #size-cells properties

arm64/xen: Add missing #address-cells and #size-cells properties

The properties #address-cells and #size-cells are used to know the
number of cells for ranges provided by "regs". If they don't exist, the
value are resp. 2 and 1.

Currently, when multiboot nodes are created it is assumed that #address-cells
and #size-cells are exactly 2. However, they are never set by GRUB and
will result to later failure when the device-tree is generated by GRUB
or contain different values.

To prevent this failure, create the both properties in the chosen nodes.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>