spi: dt-bindings: Add an example with two stacked flashes

Provide an example of how to describe two flashes in eg. stacked mode.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220126112608.955728-4-miquel.raynal@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-controller.yaml

@@ -139,4 +139,11 @@ examples:
             spi-max-frequency = <100000>;
             reg = <1>;
         };
+
+        flash@2 {
+          compatible = "jedec,spi-nor";
+          spi-max-frequency = <50000000>;
+          reg = <2>, <3>;
+          stacked-memories = /bits/ 64 <0x10000000 0x10000000>;
+        };
     };