dt-bindings: gpio: Update DT binding docs to support SiFive FU740 SoC

Add new compatible strings to the DT binding documents to support SiFive
FU740-C000.
Signed-off-by: Yash Shah <yash.shah@sifive.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Documentation/devicetree/bindings/gpio/sifive,gpio.yaml

@@ -13,7 +13,9 @@ maintainers:
 properties:
   compatible:
     items:
-      - const: sifive,fu540-c000-gpio
+      - enum:
+          - sifive,fu540-c000-gpio
+          - sifive,fu740-c000-gpio
       - const: sifive,gpio0
 
   reg: