dt-bindings: remoteproc: stm32: add wakeup-source property

If the optional wdg interrupt is defined, then this property
may be defined.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/remoteproc/st,stm32-rproc.yaml

@@ -50,6 +50,8 @@ properties:
     description: Should contain the WWDG1 watchdog reset interrupt
     maxItems: 1
 
+  wakeup-source: true
+
   mboxes:
     description:
       This property is required only if the rpmsg/virtio functionality is used.