gpio: bcm-kona: make irq_chip immutable

The gpiolib is moving to make irq_chip immutable, otherwise
there is warning: "not an immutable chip, please consider fixing it!"

The bcm_gpio_irq_chip already has irq hooks configured correctly,
bcm_kona_gpio_irq_mask/bcm_kona_gpio_irq_unmask calls gpiochip_disable_irq/
gpiochip_enable_irq, and bcm_kona_gpio_irq_reqres/irq_release_resources
calls gpiochip_reqres_irq/gpiochip_relres_irq.

So just need to  flag it as IRQCHIP_IMMUTABLE.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250509-gpio-v1-1-639377c98288@nxp.com


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>