dt-bindings: arm: stm32: Convert stm32-syscon to json-schema

Convert the STM32 syscon binding to DT schema format using json-schema.
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/stm32/st,stm32-syscon.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/arm/stm32/st,stm32-syscon.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: STMicroelectronics STM32 Platforms System Controller bindings
+
+maintainers:
+  - Alexandre Torgue <alexandre.torgue@st.com>
+  - Christophe Roullier <christophe.roullier@st.com>
+
+properties:
+  compatible:
+    oneOf:
+      - items:
+        - enum:
+          - st,stm32mp157-syscfg
+        - const: syscon
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+
+examples:
+  - |
+    #include <dt-bindings/clock/stm32mp1-clks.h>
+    syscfg: syscon@50020000 {
+        compatible = "st,stm32mp157-syscfg", "syscon";
+        reg = <0x50020000 0x400>;
+        clocks = <&rcc SYSCFG>;
+    };
+
+...

Documentation/devicetree/bindings/arm/stm32/stm32-syscon.txt

-STMicroelectronics STM32 Platforms System Controller
-
-Properties:
-   - compatible : should contain two values. First value must be :
-                 - " st,stm32mp157-syscfg " - for stm32mp157 based SoCs,
-                 second value must be always "syscon".
-   - reg : offset and length of the register set.
-   - clocks: phandle to the syscfg clock
-
- Example:
-         syscfg: syscon@50020000 {
-                 compatible = "st,stm32mp157-syscfg", "syscon";
-                 reg = <0x50020000 0x400>;
-                 clocks = <&rcc SYSCFG>;
-         };
-