dt-bindings: interrupt-controller: arm,gic: Document resets property

A generic GIC block embedded in an SoC may be connected to an on-SoC
reset controller.  Hence allow the DTS writer to describe this relation,
by documenting the optional presence of a "reset" property.

This gets rid of "make dtbs_check" warnings like:

    arch/arm/boot/dts/r8a7791-porter.dt.yaml: interrupt-controller@f1001000: 'resets' does not match any of the regexes: '^v2m@[0-9a-f]+$', 'pinctrl-[0-9]+'
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/interrupt-controller/arm,gic.yaml

@@ -131,6 +131,9 @@ properties:
   power-domains:
     maxItems: 1
 
+  resets:
+    maxItems: 1
+
 required:
   - compatible
   - reg