dt-bindings: mailbox: convert bcm2835-mbox bindings to YAML

Convert the DT binding document for bcm2835-mbox from .txt to YAML.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

Documentation/devicetree/bindings/mailbox/brcm,bcm2835-mbox.txt

-Broadcom BCM2835 VideoCore mailbox IPC
-
-Required properties:
-
-- compatible:	Should be "brcm,bcm2835-mbox"
-- reg:		Specifies base physical address and size of the registers
-- interrupts:	The interrupt number
-		  See bindings/interrupt-controller/brcm,bcm2835-armctrl-ic.txt
-- #mbox-cells:	Specifies the number of cells needed to encode a mailbox
-		  channel. The value shall be 0, since there is only one
-		  mailbox channel implemented by the device.
-
-Example:
-
-mailbox: mailbox@7e00b880 {
-	compatible = "brcm,bcm2835-mbox";
-	reg = <0x7e00b880 0x40>;
-	interrupts = <0 1>;
-	#mbox-cells = <0>;
-};
-
-firmware: firmware {
-	compatible = "raspberrypi,firmware";
-	mboxes = <&mailbox>;
-	#power-domain-cells = <1>;
-};

Documentation/devicetree/bindings/mailbox/brcm,bcm2835-mbox.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/brcm,bcm2835-mbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom BCM2835 VideoCore mailbox IPC
+
+maintainers:
+  - Stefan Wahren <stefan.wahren@i2se.com>
+
+properties:
+  compatible:
+    const: brcm,bcm2835-mbox
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  "#mbox-cells":
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - "#mbox-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    mailbox@7e00b880 {
+      compatible = "brcm,bcm2835-mbox";
+      reg = <0x7e00b880 0x40>;
+      interrupts = <0 1>;
+      #mbox-cells = <0>;
+    };