[DNM] dts: bindings: cpus,cluster: add #ranges-flags-cells

Currently under discussion in
devicetree-org/lopper#161

Do not merge until discussion finalizes.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

dts/bindings/sys/cpus,cluster.yaml

@@ -36,6 +36,14 @@ properties:
     description: |
       The number of cells required to represent the size of an
       address range in an address-map entry.
+  "#ranges-flags-cells":
+    type: int
+    default: 0
+    description: |
+      The number of cells required to represent the flags field
+      in an address-map entry. The default 0 assumes there are no
+      flags; this value is defined in the system devicetree
+      specification.
   address-map:
     type: compound
     required: true