dt-bindings: mfd/syscon: Add resets property

Simple syscon devices may require deassertion of a reset signal in order
to access their register set. This change adds the `resets` property from
reset.yaml#/properties/resets (referenced through core.yaml), specifying
a maxItems of 1 for a single (optional) reset descriptor.

This will allow a future change to the syscon driver to implement reset
control.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230105005010.124948-2-jk@codeconstruct.com.au

Documentation/devicetree/bindings/mfd/syscon.yaml

@@ -89,6 +89,9 @@ properties:
       on the device.
     enum: [1, 2, 4, 8]
 
+  resets:
+    maxItems: 1
+
   hwlocks:
     maxItems: 1
     description: