dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

Add compatible strings for MediaTek SoCs where the hardware random number
generator is accessed via a vendor-defined Secure Monitor Call (SMC)
rather than direct MMIO register access:

  - mediatek,mt7981-rng
  - mediatek,mt7987-rng
  - mediatek,mt7988-rng

These variants require no reg, clocks, or clock-names properties since
the RNG hardware is managed by ARM Trusted Firmware-A.

Relax the $nodename pattern to also allow 'rng' in addition to the
existing 'rng@...' pattern.

Add a second example showing the minimal SMC variant binding.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/mtk-rng.yaml

@@ -11,12 +11,13 @@ maintainers:
 
 properties:
   $nodename:
-    pattern: "^rng@[0-9a-f]+$"
+    pattern: "^rng(@[0-9a-f]+)?$"
 
   compatible:
     oneOf:
       - enum:
           - mediatek,mt7623-rng
+          - mediatek,mt7981-rng
       - items:
           - enum:
               - mediatek,mt7622-rng
@@ -25,6 +26,11 @@ properties:
               - mediatek,mt8365-rng
               - mediatek,mt8516-rng
           - const: mediatek,mt7623-rng
+      - items:
+          - enum:
+              - mediatek,mt7987-rng
+              - mediatek,mt7988-rng
+          - const: mediatek,mt7981-rng
 
   reg:
     maxItems: 1
@@ -38,9 +44,23 @@ properties:
 
 required:
   - compatible
-  - reg
-  - clocks
-  - clock-names
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: mediatek,mt7981-rng
+    then:
+      properties:
+        reg: false
+        clocks: false
+        clock-names: false
+    else:
+      required:
+        - reg
+        - clocks
+        - clock-names
 
 additionalProperties: false
 
@@ -54,3 +74,7 @@ examples:
         clocks = <&infracfg CLK_INFRA_TRNG>;
         clock-names = "rng";
     };
+  - |
+    rng {
+        compatible = "mediatek,mt7981-rng";
+    };