dt-bindings: rtc: microcrystal,rv3032: Document wakeup-source property

The RV3032 can be used as a wake-up source, document the 'wakeup-source'
property as allowed property.

Signed-off-by: Marek Vasut <marex@denx.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230921192604.70944-1-marex@denx.de
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/microcrystal,rv3032.yaml

@@ -38,6 +38,8 @@ properties:
       - 3000
       - 4400
 
+  wakeup-source: true
+
 required:
   - compatible
   - reg