dt-bindings: mailbox: Convert apm,xgene-slimpro-mbox to DT schema

new file mode 100644
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+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/apm,xgene-slimpro-mbox.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: APM X-Gene SLIMpro mailbox
+
+maintainers:
+  - Khuong Dinh <[email protected]>
+
+description:
+  The APM X-Gene SLIMpro mailbox is used to communicate messages between
+  the ARM64 processors and the Cortex M3 (dubbed SLIMpro). It uses a simple
+  interrupt based door bell mechanism and can exchange simple messages using the
+  internal registers.
+
+properties:
+  compatible:
+    const: apm,xgene-slimpro-mbox
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    items:
+      - description: mailbox channel 0 doorbell
+      - description: mailbox channel 1 doorbell
+      - description: mailbox channel 2 doorbell
+      - description: mailbox channel 3 doorbell
+      - description: mailbox channel 4 doorbell
+      - description: mailbox channel 5 doorbell
+      - description: mailbox channel 6 doorbell
+      - description: mailbox channel 7 doorbell
+
+  '#mbox-cells':
+    description: Number of mailbox channel.
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - '#mbox-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    mailbox@10540000 {
+        compatible = "apm,xgene-slimpro-mbox";
+        reg = <0x10540000 0xa000>;
+        #mbox-cells = <1>;
+        interrupts = <0x0 0x0 0x4>,
+                     <0x0 0x1 0x4>,
+                     <0x0 0x2 0x4>,
+                     <0x0 0x3 0x4>,
+                     <0x0 0x4 0x4>,
+                     <0x0 0x5 0x4>,
+                     <0x0 0x6 0x4>,
+                     <0x0 0x7 0x4>;
+    };

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-The APM X-Gene SLIMpro mailbox is used to communicate messages between
-the ARM64 processors and the Cortex M3 (dubbed SLIMpro). It uses a simple
-interrupt based door bell mechanism and can exchange simple messages using the
-internal registers.
-
-There are total of 8 interrupts in this mailbox. Each used for an individual
-door bell (or mailbox channel).
-
-Required properties:
-- compatible:	Should be as "apm,xgene-slimpro-mbox".
-
-- reg:		Contains the mailbox register address range.
-
-- interrupts:	8 interrupts must be from 0 to 7, interrupt 0 define the
-		the interrupt for mailbox channel 0 and interrupt 1 for
-		mailbox channel 1 and so likewise for the reminder.
-
-- #mbox-cells:	only one to specify the mailbox channel number.
-
-Example:
-
-Mailbox Node:
-		mailbox: mailbox@10540000 {
-			compatible = "apm,xgene-slimpro-mbox";
-			reg = <0x0 0x10540000 0x0 0xa000>;
-			#mbox-cells = <1>;
-			interrupts =  	<0x0 0x0 0x4>,
-					<0x0 0x1 0x4>,
-					<0x0 0x2 0x4>,
-					<0x0 0x3 0x4>,
-					<0x0 0x4 0x4>,
-					<0x0 0x5 0x4>,
-					<0x0 0x6 0x4>,
-					<0x0 0x7 0x4>,
-		};