pinctrl: nuvoton: Convert to use struct pingroup and PINCTRL_PINGROUP()

The pin control header provides struct pingroup and PINCTRL_PINGROUP() macro.
Utilize them instead of open coded variants 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/r/20231204160033.1872569-6-andriy.shevchenko@linux.intel.com


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