dt-bindings: rng: document Silex Insight BA431 hwrng

This patch documents the device tree bindings of the BA431 hardware
random number generator.

This IP is for instance present in the Viper OEM boards sold by Silex
Insight.
Signed-off-by: Olivier Sobrie <olivier.sobrie@silexinsight.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/silex-insight,ba431-rng.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rng/silex-insight,ba431-rng.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Silex Insight BA431 RNG bindings
+
+description: |
+  The BA431 hardware random number generator is an IP that is FIPS-140-2/3
+  certified.
+
+maintainers:
+  - Olivier Sobrie <olivier.sobrie@silexinsight.com>
+
+properties:
+  compatible:
+    const: silex-insight,ba431-rng
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    rng@42800000 {
+      compatible = "silex-insight,ba431-rng";
+      reg = <0x42800000 0x1000>;
+    };
+
+...