ASoC: dt-bindings: qcom,q6apm-dai: add memory-region and relax iommus

On modem-DSP (mDSP) platforms the DSP runs in a stage-2 protected
context and cannot use the SMMU. PCM buffers must live in reserved-memory
carveouts that are SCM-assigned to the appropriate VMIDs.

Add a memory-region property (1-2 entries) for the control-path and
data-path carveouts, and require q6apm-dais nodes to describe exactly
one access path: iommus for SMMU-backed systems or memory-region for
mDSP systems. Remove iommus from the common required list since mDSP
platforms have neither IOMMU nor VMID DT properties.

Signed-off-by: Ajay Kumar Nandam <ajay.nandam@oss.qualcomm.com>
Link: https://patch.msgid.link/20260923-vmid-v4-v6-3-3d61a0319b1c@oss.qualcomm.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/qcom,q6apm-dai.yaml

@@ -20,9 +20,24 @@ properties:
     minItems: 1
     maxItems: 2
 
+  memory-region:
+    minItems: 1
+    items:
+      - description:
+          Control-path buffer (audio_heap_mem) for platforms where the DSP
+          runs in a stage-2 protected context (e.g. modem-DSP).
+      - description:
+          Data-path buffer pool from which per-stream DMA buffers are
+          allocated.
+
 required:
   - compatible
-  - iommus
+
+oneOf:
+  - required:
+      - iommus
+  - required:
+      - memory-region
 
 additionalProperties: false