dt-bindings: gpio: fsl-imx-gpio: Document imx25 and imx27

fsl,imx25-gpio and fsl,imx27-gpio are not documented, causing schema
warnings.

fsl,imx25-gpio is compatible with fsl,imx35-gpio and fsl,imx27-gpio
is compatible with fsl,imx21-gpio.

Document them accordingly.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/fsl-imx-gpio.yaml

@@ -18,9 +18,17 @@ properties:
           - fsl,imx31-gpio
           - fsl,imx35-gpio
           - fsl,imx7d-gpio
+      - items:
+          - enum:
+              - fsl,imx27-gpio
+          - const: fsl,imx21-gpio
       - items:
           - const: fsl,imx35-gpio
           - const: fsl,imx31-gpio
+      - items:
+          - enum:
+              - fsl,imx25-gpio
+          - const: fsl,imx35-gpio
       - items:
           - enum:
               - fsl,imx50-gpio