dt-bindings: pwm: convert pwm-bcm2835 bindings to YAML

Convert the DT binding document for pwm-bcm2835 from .txt to YAML.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/pwm-bcm2835.txt

-BCM2835 PWM controller (Raspberry Pi controller)
-
-Required properties:
-- compatible: should be "brcm,bcm2835-pwm"
-- reg: physical base address and length of the controller's registers
-- clocks: This clock defines the base clock frequency of the PWM hardware
-  system, the period and the duty_cycle of the PWM signal is a multiple of
-  the base period.
-- #pwm-cells: Should be 3. See pwm.yaml in this directory for a description of
-  the cells format.
-
-Examples:
-
-pwm@2020c000 {
-	compatible = "brcm,bcm2835-pwm";
-	reg = <0x2020c000 0x28>;
-	clocks = <&clk_pwm>;
-	#pwm-cells = <3>;
-};
-
-clocks {
-	....
-		clk_pwm: pwm {
-			compatible = "fixed-clock";
-			reg = <3>;
-			#clock-cells = <0>;
-			clock-frequency = <9200000>;
-		};
-	....
-};

Documentation/devicetree/bindings/pwm/pwm-bcm2835.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/pwm-bcm2835.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: BCM2835 PWM controller (Raspberry Pi controller)
+
+maintainers:
+  - Stefan Wahren <stefan.wahren@i2se.com>
+
+allOf:
+  - $ref: pwm.yaml#
+
+properties:
+  compatible:
+    const: brcm,bcm2835-pwm
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  "#pwm-cells":
+    const: 3
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - "#pwm-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    pwm@2020c000 {
+      compatible = "brcm,bcm2835-pwm";
+      reg = <0x2020c000 0x28>;
+      clocks = <&clk_pwm>;
+      #pwm-cells = <3>;
+    };