dt-bindings: Add en7523-scu device tree binding documentation

Adds device tree binding documentation for clocks in the EN7523 SOC.

Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: John Crispin <[e-mail]>
Signed-off-by: Felix Fietkau <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/clock/airoha,en7523-scu.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/airoha,en7523-scu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: EN7523 Clock Device Tree Bindings
+
+maintainers:
+  - Felix Fietkau <[e-mail]>
+  - John Crispin <[e-mail]>
+
+description: |
+  This node defines the System Control Unit of the EN7523 SoC,
+  a collection of registers configuring many different aspects of the SoC.
+
+  The clock driver uses it to read and configure settings of the
+  PLL controller, which provides clocks for the CPU, the bus and
+  other SoC internal peripherals.
+
+  Each clock is assigned an identifier and client nodes use this identifier
+  to specify which clock they consume.
+
+  All these identifiers can be found in:
+  [1]: <include/dt-bindings/clock/en7523-clk.h>.
+
+  The clocks are provided inside a system controller node.
+
+properties:
+  compatible:
+    items:
+      - const: airoha,en7523-scu
+
+  reg:
+    maxItems: 2
+
+  "#clock-cells":
+    description:
+      The first cell indicates the clock number, see [1] for available
+      clocks.
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/en7523-clk.h>
+    scu: system-controller@1fa20000 {
+      compatible = "airoha,en7523-scu";
+      reg = <0x1fa20000 0x400>,
+            <0x1fb00000 0x1000>;
+      #clock-cells = <1>;
+    };

include/dt-bindings/clock/en7523-clk.h

···
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
+
+#ifndef _DT_BINDINGS_CLOCK_AIROHA_EN7523_H_
+#define _DT_BINDINGS_CLOCK_AIROHA_EN7523_H_
+
+#define EN7523_CLK_GSW		0
+#define EN7523_CLK_EMI		1
+#define EN7523_CLK_BUS		2
+#define EN7523_CLK_SLIC		3
+#define EN7523_CLK_SPI		4
+#define EN7523_CLK_NPU		5
+#define EN7523_CLK_CRYPTO	6
+#define EN7523_CLK_PCIE		7
+
+#define EN7523_NUM_CLOCKS	8
+
+#endif /* _DT_BINDINGS_CLOCK_AIROHA_EN7523_H_ */