dt-bindings: gpio: gpio-vf610: Add imx8ulp compatible string

Add the compatible string for i.MX8ULP.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>