dt-bindings: timer: Add renesas,em-sti bindings

Document Device Tree bindings for the Renesas EMMA Mobile System Timer.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200519081101.28973-1-geert+renesas@glider.be

Documentation/devicetree/bindings/timer/renesas,em-sti.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/timer/renesas,em-sti.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Renesas EMMA Mobile System Timer
+
+maintainers:
+  - Magnus Damm <magnus.damm@gmail.com>
+
+properties:
+  compatible:
+    const: renesas,em-sti
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: sclk
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    timer@e0180000 {
+            compatible = "renesas,em-sti";
+            reg = <0xe0180000 0x54>;
+            interrupts = <GIC_SPI 125 IRQ_TYPE_LEVEL_HIGH>;
+            clocks = <&sti_sclk>;
+            clock-names = "sclk";
+    };