pinctrl: nuvoton: Make use of struct pinfunction and PINCTRL_PINFUNCTION()

Since pin control provides a generic data type and a macro for
the pin function definition, use them in the driver.

Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/20250318105932.2090926-4-andriy.shevchenko@linux.intel.com


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