ASoC: dt-bindings: tegra: Add iommus property to Tegra graph card

Document 'iommus' property for APE (Audio Processing Engine) sound
card.
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Link: https://lore.kernel.org/r/1611944866-29373-3-git-send-email-spujar@nvidia.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/nvidia,tegra-audio-graph-card.yaml

@@ -45,6 +45,9 @@ properties:
     minItems: 1
     maxItems: 3
 
+  iommus:
+    maxItems: 1
+
 required:
   - clocks
   - clock-names