dt-bindings: clock: document the fsl-flexspi-clk device

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201108185113.31377-7-michael@walle.cc
[sboyd@kernel.org: DT bindings aren't drivers]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/fsl,flexspi-clock.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/fsl,flexspi-clock.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Freescale FlexSPI clock driver for Layerscape SoCs
+
+maintainers:
+  - Michael Walle <michael@walle.cc>
+
+description:
+  The Freescale Layerscape SoCs have a special FlexSPI clock which is
+  derived from the platform PLL.
+
+properties:
+  compatible:
+    enum:
+      - fsl,ls1028a-flexspi-clk
+      - fsl,lx2160a-flexspi-clk
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  '#clock-cells':
+    const: 0
+
+  clock-output-names:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    dcfg {
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        fspi_clk: clock-controller@900 {
+            compatible = "fsl,ls1028a-flexspi-clk";
+            reg = <0x900 0x4>;
+            #clock-cells = <0>;
+            clocks = <&parentclk>;
+            clock-output-names = "fspi_clk";
+        };
+    };