dt-bindings: gpio: fsl-imx-gpio: Add parsing of hogs

Allow parsing GPIO controller children nodes with GPIO hogs to fix
warning:

  arch/arm64/boot/dts/freescale/imx8mq-evk.dt.yaml: gpio@30240000: 'wl-reg-on' does not match any of the regexes: 'pinctrl-[0-9]+'
    From schema: Documentation/devicetree/bindings/gpio/fsl-imx-gpio.yaml

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200825193536.7332-4-krzk@kernel.org