dt-bindings: iommu: renesas,ipmmu-vmsa: Make 'power-domains' conditionally required

Fixing the compatible string typos results in an error in the example:

Documentation/devicetree/bindings/iommu/renesas,ipmmu-vmsa.example.dt.yaml:
  iommu@fe951000: 'power-domains' is a required property

Based on the dts files, a 'power-domains' property only exists on Gen 3
which can be conditioned on !renesas,ipmmu-vmsa.

Cc: Joerg Roedel <joro@8bytes.org>
Cc: Will Deacon <will@kernel.org>
Cc: iommu@lists.linux-foundation.org
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210202205544.24812-2-robh@kernel.org

Documentation/devicetree/bindings/iommu/renesas,ipmmu-vmsa.yaml

@@ -76,7 +76,6 @@ required:
   - compatible
   - reg
   - '#iommu-cells'
-  - power-domains
 
 oneOf:
   - required:
@@ -86,6 +85,17 @@ oneOf:
 
 additionalProperties: false
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              const: renesas,ipmmu-vmsa
+    then:
+      required:
+        - power-domains
+
 examples:
   - |
     #include <dt-bindings/clock/r8a7791-cpg-mssr.h>