dt-bindings: add device tree binding for Arm CryptoCell trng engine

The Arm CryptoCell is a hardware security engine. This patch adds DT
bindings for its TRNG (True Random Number Generator) engine.
Signed-off-by: Hadar Gat <hadar.gat@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/devicetree/bindings/rng/arm-cctrng.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rng/arm-cctrng.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Arm TrustZone CryptoCell TRNG engine
+
+maintainers:
+  - Hadar Gat <hadar.gat@arm.com>
+
+description: |+
+  Arm TrustZone CryptoCell TRNG (True Random Number Generator) engine.
+
+properties:
+  compatible:
+    enum:
+      - arm,cryptocell-713-trng
+      - arm,cryptocell-703-trng
+
+  interrupts:
+    maxItems: 1
+
+  reg:
+    maxItems: 1
+
+  arm,rosc-ratio:
+    description:
+      Arm TrustZone CryptoCell TRNG engine has 4 ring oscillators.
+      Sampling ratio values for these 4 ring oscillators. (from calibration)
+    allOf:
+      - $ref: /schemas/types.yaml#/definitions/uint32-array
+      - items:
+          maxItems: 4
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - interrupts
+  - reg
+  - arm,rosc-ratio
+
+additionalProperties: false
+
+examples:
+  - |
+    arm_cctrng: rng@60000000 {
+        compatible = "arm,cryptocell-713-trng";
+        interrupts = <0 29 4>;
+        reg = <0x60000000 0x10000>;
+        arm,rosc-ratio = <5000 1000 500 0>;
+    };