dt-bindings: arm: samsung: Update the CHIPID binding for ASV

This patch adds documentation of new optional "samsung,asv-bin"
property in the chipid device node and documents requirement of
"syscon" compatible string.  These additions are needed to support
Exynos ASV (Adaptive Supply Voltage) feature.
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
[robh: drop 'select' which is no longer needed. Fix up example whitespace]
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/samsung/exynos-chipid.yaml

@@ -13,13 +13,28 @@ properties:
   compatible:
     items:
       - const: samsung,exynos4210-chipid
+      - const: syscon
 
   reg:
     maxItems: 1
 
+  samsung,asv-bin:
+    description:
+      Adaptive Supply Voltage bin selection. This can be used
+      to determine the ASV bin of an SoC if respective information
+      is missing in the CHIPID registers or in the OTP memory.
+    allOf:
+      - $ref: /schemas/types.yaml#/definitions/uint32
+      - enum: [ 0, 1, 2, 3 ]
+
+required:
+  - compatible
+  - reg
+
 examples:
   - |
     chipid@10000000 {
-        compatible = "samsung,exynos4210-chipid";
+        compatible = "samsung,exynos4210-chipid", "syscon";
         reg = <0x10000000 0x100>;
+        samsung,asv-bin = <2>;
     };