pinctrl: nuvoton: wpcm450: Convert irqchip to IRQCHIP_IMMUTABLE

Commit 6c846d02 ("gpio: Don't fiddle with irqchips marked as
immutable") added a warning for irqchips that are not marked with
IRQCHIP_IMMUTABLE.

Convert the pinctrl-wpcm450 driver to an immutable irqchip.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20221031222833.201322-1-j.neuschaefer@gmx.net


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>