dt-bindings: ehci/ohci: Allow iommus property

A OHCI/EHCI controller could be behind an IOMMU, in which case an iommus
property assigns the stream ID for this device.

Allow that property in the DT bindings to fix a complaint about the Arm Juno
board's DTS file.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/usb/generic-ehci.yaml

@@ -88,6 +88,9 @@ properties:
   phy-names:
     const: usb
 
+  iommus:
+    maxItems: 1
+
 required:
   - compatible
   - reg

Documentation/devicetree/bindings/usb/generic-ohci.yaml

@@ -76,6 +76,9 @@ properties:
   phy-names:
     const: usb
 
+  iommus:
+    maxItems: 1
+
 required:
   - compatible
   - reg