dt-bindings: timer: Add Nomadik MTU binding

The Nomadik MTU timer has been used in devicetrees forever
but somehow we missed to add a binding for it. Fix it
by simply adding it.

Cc: Lee Jones <lee.jones@linaro.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220526213621.373727-1-linus.walleij@linaro.orgSigned-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/st,nomadik-mtu.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# Copyright 2022 Linaro Ltd.
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/timer/st,nomadik-mtu.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: ST Microelectronics Nomadik Multi-Timer Unit MTU Timer
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: This timer is found in the ST Microelectronics Nomadik
+  SoCs STn8800, STn8810 and STn8815 as well as in ST-Ericsson DB8500.
+
+properties:
+  compatible:
+    items:
+      - const: st,nomadik-mtu
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    description: The first clock named TIMCLK clocks the actual timers and
+      the second clock clocks the digital interface to the interconnect.
+    maxItems: 2
+
+  clock-names:
+    items:
+      - const: timclk
+      - const: apb_pclk
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/mfd/dbx500-prcmu.h>
+    timer@a03c6000 {
+      compatible = "st,nomadik-mtu";
+      reg = <0xa03c6000 0x1000>;
+      interrupts = <GIC_SPI 4 IRQ_TYPE_LEVEL_HIGH>;
+
+      clocks = <&prcmu_clk PRCMU_TIMCLK>, <&prcc_pclk 6 6>;
+      clock-names = "timclk", "apb_pclk";
+    };