dt-bindings: mfd: khadas: Add new compatible for Khadas VIM4 MCU

The Khadas VIM4 MCU register is slightly different
from previous boards' MCU.
This board also features a switchable power source for its fan.

Signed-off-by: Ronald Claveau <linux-kernel-dev@aliel.fr>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260421-add-mcu-fan-khadas-vim4-v4-1-447114a28f2d@aliel.fr
Signed-off-by: Lee Jones <lee@kernel.org>

Documentation/devicetree/bindings/mfd/khadas,mcu.yaml

@@ -18,6 +18,7 @@ properties:
   compatible:
     enum:
       - khadas,mcu # MCU revision is discoverable
+      - khadas,vim4-mcu # Different MCU variant, not discoverable
 
   "#cooling-cells": # Only needed for boards having FAN control feature
     const: 2
@@ -25,10 +26,27 @@ properties:
   reg:
     maxItems: 1
 
+  fan-supply:
+    description: Phandle to the regulator that powers the fan.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
 required:
   - compatible
   - reg
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: khadas,vim4-mcu
+    then:
+      required:
+        - fan-supply
+    else:
+      properties:
+        fan-supply: false
+
 additionalProperties: false
 
 examples: