dt-bindings: mailbox: Convert marvell,armada-3700-rwtm-mailbox to DT schema

Convert the Marvell Armada 3700 rWTM mailbox binding to DT schema
format. It's a straightforward conversion.

Link: https://lore.kernel.org/r/20250812181357.63395-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/mailbox/marvell,armada-3700-rwtm-mailbox.txt

@@ -1,16 +0,0 @@
-* rWTM BIU Mailbox driver for Armada 37xx
-
-Required properties:
-- compatible:	must be "marvell,armada-3700-rwtm-mailbox"
-- reg:		physical base address of the mailbox and length of memory mapped
-		region
-- interrupts:	the IRQ line for the mailbox
-- #mbox-cells:	must be 1
-
-Example:
-	rwtm: mailbox@b0000 {
-		compatible = "marvell,armada-3700-rwtm-mailbox";
-		reg = <0xb0000 0x100>;
-		interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>;
-		#mbox-cells = <1>;
-	};

Documentation/devicetree/bindings/mailbox/marvell,armada-3700-rwtm-mailbox.yaml

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/marvell,armada-3700-rwtm-mailbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Marvell Armada 3700 rWTM Mailbox
+
+maintainers:
+  - Marek Behún <kabel@kernel.org>
+
+properties:
+  compatible:
+    const: marvell,armada-3700-rwtm-mailbox
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  '#mbox-cells':
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - '#mbox-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    mailbox@b0000 {
+        compatible = "marvell,armada-3700-rwtm-mailbox";
+        reg = <0xb0000 0x100>;
+        interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>;
+        #mbox-cells = <1>;
+    };