dt-bindings: clock: Add binding documentation for TI EHRPWM TBCLK

Add DT bindings for TI EHRPWM's TimeBase clock (TBCLK) on TI's AM654 SoC.
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lkml.kernel.org/r/20200227053529.16479-2-vigneshr@ti.comReviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/ti,am654-ehrpwm-tbclk.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/ti,am654-ehrpwm-tbclk.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: TI EHRPWM Time Base Clock
+
+maintainers:
+  - Vignesh Raghavendra <vigneshr@ti.com>
+
+properties:
+  compatible:
+    items:
+      - const: ti,am654-ehrpwm-tbclk
+      - const: syscon
+
+  "#clock-cells":
+    const: 1
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - "#clock-cells"
+  - reg
+
+examples:
+  - |
+    ehrpwm_tbclk: syscon@4140 {
+        compatible = "ti,am654-ehrpwm-tbclk", "syscon";
+        reg = <0x4140 0x18>;
+        #clock-cells = <1>;
+    };