xen/arm: vITS: add #msi-cells property

Non-PCI platform devices may use the ITS. Dom0 Linux drivers for such
devices are failing to register IRQs due to a missing #msi-cells
property. Add the missing #msi-cells property.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Rahul Singh <rahul.singh@arm.com>

xen/arch/arm/gic-v3-its.c

@@ -951,6 +951,10 @@ int gicv3_its_make_hwdom_dt_nodes(const struct domain *d,
         if ( res )
             return res;
 
+        res = fdt_property_cell(fdt, "#msi-cells", 1);
+        if ( res )
+            return res;
+
         if ( its->phandle )
         {
             res = fdt_property_cell(fdt, "phandle", its->phandle);