dt-bindings: ata: snps,dwc-ahci: Allow 'iommus' property

The AMD Seattle DWC AHCI is behind an IOMMU and has 1-3 entries, so add
the 'iommus' property. There's not a specific compatible, so we can't
limit it to Seattle.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>

Documentation/devicetree/bindings/ata/snps,dwc-ahci.yaml

@@ -33,6 +33,10 @@ properties:
       - description: SPEAr1340 AHCI SATA device
         const: snps,spear-ahci
 
+  iommus:
+    minItems: 1
+    maxItems: 3
+
 patternProperties:
   "^sata-port@[0-9a-e]$":
     $ref: /schemas/ata/snps,dwc-ahci-common.yaml#/$defs/dwc-ahci-port